Welding Guide
1
Image courtesy of Kemppi.
Ovako develops high-tech steel solutions for,
and in cooperation with, its customers in the
bearing, transport and manufacturing industries. Our steel makes our customers’ end
products more resilient and extends their useful life, ultimately resulting in smarter, more
energy-efficient and more environmentally
friendly products.
Our production is based on recycled scrap and
includes steel in the form of bar, tube, ring and
pre-components. Ovako has around 3,000
employees in more than 30 countries and sales
of approximately EUR 1 billion. In June 2018
Ovako became a subsidiary within the Japanese Nippon Steel Corporation group, one of
the world’s largest steel producers. For more
information, please visit us at www.ovako.com
and www.nipponsteel.com
TABLE OF CONTENTS
1
INTRODUCTION
4
2
WELD REGIONS
5
3
3.1
3.2
3.3
3.4
3.5
3.6
HEAT AFFECTED ZONE
Cooling rate
Plate thickness and joint type
Arc energy and effective heat input
Working temperature
Hardenability
Microstructural changes
7
7
9
10
11
12
13
4
4.1
4.1.1
4.1.2
4.1.3
4.1.4
4.1.5
4.2
4.3
WELDABILITY
Cold cracking
Microstructure
Hydrogen content
Stresses
Temperature
Preventing cold cracking
Hot cracking
Lamellar tearing
15
15
15
16
17
17
17
18
19
5
5.1
5.2
5.3
5.4
5.5
5.6
5.7
WELD DEFECTS
Pores
Slag inclusions
Lack of fusion
Incomplete penetration
Spatter and poor arc starts
Shrinkage cavity (or pipe)
Undercut
20
20
20
21
21
22
22
22
6
6.1
6.2
6.3
FEATURES OF A WELD JOINT
Static strength
Fatigue strength
Impact toughness
23
23
23
24
7
7.1
WELD DISTORTIONS
25
Longitudinal and transverse
distortions
25
Tack welding and welding sequence 26
Flame straightening
26
7.2
7.3
8
8.1
8.2
8.3
8.4
8.4.1
8.4.2
WELDING OF DIFFERENT
STEEL GRADES
General structural steels
Machine steels
High strength structural steels
Quenching and tempering steels
Welding of quenching and
tempering steels
Welding of the IMACRO
27
28
29
31
35
8.5
8.6
8.7
Case hardening steels
Boron steels
Spring steels
43
45
47
9
REPAIR WELDING OF
PROBLEM STEELS
50
10
10.1
JOINT WELDING OF NON-ALLOYED
AND STAINLESS STEEL
52
Example of use
53
11
HARDFACING
12
EXAMPLES OF WELDING
THE OVAKO STEELS
12.1
Flange axle
12.2 Torsion bar
12.3 Repair welding of an axle
12.4 Gear
12.5 Lifting pin for vessel’s plate
12.6 Piston rod
12.7
Piston
12.8 Valve head
12.9 Welding a stainless spindle
to lever arm
12.10 Steering joint
12.11 Joint
12.12 Track link A
12.13 Track link B
12.14 Welded beam
12.15 Welding a crane rail to beam
12.16 Support wheels, rolls
12.17 Corrector lever’s surfacing
12.18 Shovel loader’s wear plate
12.19 Axles’s temporary repair weld
12.20 Gear tooth’s temporary repair weld
12.21 Example of friction welding
54
56
57
59
60
61
62
63
64
65
66
68
69
70
71
72
74
76
78
79
80
81
82
13
WELDING STANDARDS
14
GOOD WORKING ENVIRONMENT
ENHANCES PRODUCTIVITY
85
Industrial safety in welding
85
Welding fumes
85
Radiation and noise
85
Minimizing the risk of accidents
85
14.1
14.2
14.3
14.4
83
36
37
3
1 – INTRODUCTION
Welding is the most common way of joining
steels together. It is a metallurgic event where
steel is melted, mixed, solidified and heat
treated.
Usually the welding becomes more challenging as the steel’s strength and/or carbon and
other alloy contents increase. To achieve high
quality welds, it is important to know and
control different effects that welding causes.
These need to be taken into account before,
during and after the welding procedure itself.
Ovako focuses on bar products and therefore
this brochure covers mainly the welding of
flat and round bars. The main focus is on weldability and metallurgical features of different
steels.
The brochure also includes some practical
examples of different welded products. These
instructions are aimed to produce as high
quality and suitable weld as possible.
The given instructions and recommendations
alone do not necessarily guarantee good results. Ultimately the planner, welder and supervisor are responsible for the final quality.
Image courtesy of ESAB.
4
Back to Table of Contents
2 – WELD REGIONS
Welding causes changes in steel’s metallurgical properties. Heat melts some of the base
material and on some parts, the temperature
rises without exceeding the melting point. A
melting filler metal forms a weld pool together with a molten base material. As the
temperature drops, the weld pool solidifies
into a final weld. The heat effect causes a
distinct region to form on the base material
next to the weld. The region is better known
as a heat-affected zone, also known as a HAZ.
The different regions of weld can be seen on
figure 1.
The weld metal (1), also known as a fusion
zone, has first melted and then solidified.
It typically solidifies in an elongated form.
Between the fusion and heat-affected zone
(3-6), is a fusion boundary (2).
The heat-affected zone has been exposed to
temperatures that cause the base material’s
crystalline form to change. The closer the
area is to the weld, the higher the temperature is that it has been exposed to. The heat-affected zone can be separated into four different regions based on these temperatures.
The region closest to the weld is known as
a coarse-grained HAZ (3). This region has
been exposed to temperatures over 1100 °C,
which has caused austenite grain growth.
On a fine grained HAZ (4), the temperature
has exceeded the material’s A3 limit, causing
structural changes. On non- and low-alloy
steels, this region typically has a normalized
microstructure.
On an intercritical HAZ (5), the structure is
partially austenitized and the temperature
has been between the material’s A3- and A1
–limits.
The outermost part of the HAZ is known as
a subcritical HAZ (6). On this region where
the temperature has been more than 500 °C,
carbides begin to spheroidize and the grain
structure starts to recrystallize. Between
the heat affected zone and unaffected base
material is a zone which may have aged or in
tempered steels, annealed.
As the weld cools so do the different regions
of the heat affected zone. The temperature
changes and the rates at which they change
are based on the surrounding environment
and can be considered as miniature heat
treatments. Different structural changes in
the HAZ impact the qualities of the steel and
therefore the weld itself.
The microstructure of the HAZ, influences
particularly the likelihood of cold cracking. It
is important to control changes in this region
as they have a major effect on mechanical
qualities, especially in welds of high strength
steels and steels for low temperature conditions.
Back to Table of Contents
5
Figure 1 – Weld regions in a steel with
carbon content of 0.15%. The grain size is
significantly enlarged in the figure.
The curve T represents the maximum temperature the corresponding area of the steel
has been in. On the right side of the figure is
a part of iron-carbon phase diagram, from
which a microstructure for the each temperature can be seen. The vertical dashed line represents a steel with carbon content of 0.15%.
6
Back to Table of Contents
3 – HEAT AFFECTED ZONE
The microstructures of the heat affected zone
depend on a steel’s hardenability and cooling
environment. Hardenability depends on steel’s chemical composition.
3.1 Cooling rate
The cooling rate is given in t8/5 time, which
measures the time it takes the steel to cool
from 800 °C to 500 °C. The most crucial
changes in the steel’s microstructure take
place during this interval, while the austenite
transforms into different microstructures.
On CMn- and low alloy steels, the t8/5 cooling time can be calculated either with the
formulas given in EN 1011-2 (2001) standard
or graphically from the cooling time curves.
The 2-dimensional (1) and 3-dimensional (2)
t8/5 cooling time formulas are shown below.
The joint type factors used in the formulas
are shown in Table 1. The formulas for calculating the effective heat input are introduced
later in Chapter 3.3 Arc energy and effective
heat input.
More of the different effects of the cooling
rate are introduced later on in Chapter 3.6
Microstructural changes. The cooling rate is
an important part in determining the final
qualities of the HAZ. The main factors affecting the cooling rate are the following:
Table 1 – Joint type factors for 2- and 3-dimensional objects
Type of joint
2-dimensional (F2)
3-dimensional (F3)
Run on plate
1
1
Between runs in butt welds
0.9
0.9
Single run fillet weld on a corner-joint
0.67 to 0.9
0.67
Single run fillet weld on a T-joint
0.45 to 0.67
0.67
Back to Table of Contents
7
t8/5 = (4300-4.3*T0)*105*Q2/d2* (1/(500-T0)2-1/(800-T0)2)*F2
(1)
t8/5 = (6700-5*T0)*Q* (1/(500-T0)-1/(800-T0))*F3
(2)
where
T0 = Working temperature (°C)
Q = Heat input (kJ/mm)
d = Material thickness (mm)
F = Joint type factor (F2 or F3)
Image courtesy of ESAB.
8
Back to Table of Contents
3.2 Plate thickness and joint type
The thicker the welded material is, the faster
the heat conducts away from the weld and the
cooling rate increases. The cooling rate also
depends on the joint geometry, or in other
words, on how many different directions the
heat can conduct. The plate thickness and
joint geometry are taken into account as one
combined factor with examples shown in
Figure 2. On round bars, half of the diameter
of the bar (d/2) is equal to the wall thickness
of a plate bar, sheet or tube regarding the way
it cools.
After the certain material thickness is exceeded, the change in thickness does not
affect the heat conduction anymore, and
thickness can be treated as 3-dimensional
instead of 2-dimensional.
Figure 2 – Examples of calculating the material thickness ty: t = wall thickness of a flat
bar, sheet or tube, d = diameter of a round
tube
Back to Table of Contents
9
3.3 Arc energy and effective heat input
Energy used in arc welding is usually given
per unit of length and can be calculated with
the formula
AE = I*U
v
(3)
or
E = I*U*60 (kJ/mm)
v*1000
(4)
where
I = welding current (A)
U = arc voltage (V)T
v = arc travel speed (mm/min)
This energy is called either arc energy (AE) or
welding energy. Sometimes it is called heat
input, despite the fact that it is technically
wrong term. The effective heat input defines
the part of the arc energy which is transformed to the weld as a thermal energy. The
relation between the effective heat input and
the arc energy is the following:
Q = η*E
(5)
The efficiency factor (η) varies on each welding process. Efficiency factors of the most
common processes are the following:
MMA and MIG/MAG
TIG and plasma
SAW
10
0.8
0.6
1
Back to Table of Contents
The effective heat input depends, for example, on welding process, welding speed,
welding current, arc voltage, base material,
plate thickness and welding position. Typical
effective heat inputs for different processes
are roughly the following:
MMA
MIG/MAG
TIG
SAW
1-4 kJ/mm
0.5-3 kJ/mm
0.5-2.5 kJ/mm
2-6 kJ/mm
The higher the effective heat input is, more
thermal energy is transferred to the weld and
the cooling rate decreases.
If the steel does not have a strongly hardening structure, using a large heat input can
prevent hardening in the HAZ in certain
welds. However, using an excessive heat input reduces the steel’s impact toughness.
3.4 Working temperature
The object’s temperature during the welding
(working temperature) has a major effect
on its cooling rate. The higher the working
temperature is, the slower the cool down. As
an example, using preheating and interpass
temperatures for preventing hardening is
based on this fact.
The carbon equivalent is calculated with
the CET formula, rather than the IIW’s CEV
formula, since CET is better suited for steels
with a higher carbon content.
In multi-pass welding, the recommended
interpass temperature is the same as the preheating temperature.
The need for preheating can be determined
either graphically from the curves or mathematically with the ormula in EN 1011-2
(2001) standard shown below.
Tp = 697*CET+ 160*tanh(d/35)+62*HD0,35 + (53*CET-32)*Q-328
(6)
where
Tp = Preheating temperature (°C)
CET = Carbon equivalent = C + (Mn+Mo)/10 + (Cr+Cu)/20 + Ni/40 (%)
tanh = Hyperbolic tangent
d = Plate thickness (mm) (thickness of a single plate, not the combined thickness)
HD = Diffusible hydrogen (ml/100g deposited weld metal)
Q = Heat input (kJ/mm)
Back to Table of Contents
11
3.5 Hardenability
Hardenability describes steel’s ability to form
martensite in quenching. The ability is highly
dependent upon the steel’s chemical composition.
The main factor affecting hardenability is the
carbon content. On highly weldable steels,
the carbon content is generally limited to
0.25%. When the carbon content exceeds the
0.25% limit, special measures are required
for welding even normal material thicknesses.
Required extra procedures may include, for
example, preheating and increased working
temperature.
In addition to carbon, most of the other alloys
like manganese, chromium, nickel, molybdenum and boron increase the steel’s hardenability.
Weldability can be evaluated with a so called
equivalent carbon content (carbon equivalent, CEV or CET) which takes steel’s hardenability into account.
Steel is considered highly weldable if its CEV
value is less than 0.41.Weldability is still
considered good up until the limit of 0.45.
Steels with a carbon equivalent, CEV, over
0.45 are still weldable but with certain limitations. Values are only estimates and they do
not solely guarantee weldability since it also
depends on a base material’s thickness.
Ovako always provides a material certificate
with each delivery from which the carbon
equivalent may be easily calculated.
There are several formulas for carbon equivalent, the most common being IIW’s CEV, seen
below.
CEV = C + Mn/6 + (Cr + Mo + V)/5 + (Ni+ Cu)/15 (%)
12
Back to Table of Contents
(7)
3.6 Microstructural changes
Steels with different hardening abilities
behave differently as the cooling rate varies.
The changes can be seen by taking a look at
the so called transformation diagrams, like
the continuous cooling transformation and
time-temperature transformation diagrams.
More information on transformation diagrams
and their use can be found from the literature.
A continuous cooling transformation (CCT)
diagram is a well suited for welding purposes.
An example of the diagram is shown in Figure
3. The diagram represents changes in high
strength structural steel’s HAZ with different
cooling rates.
If the effective heat input is low in relation to
material thickness and hardenability, then
cooling that occurs quickly can cause the microstructure to become completely martensitic. Curve 1 goes from the austenite region
to the martensite region and goes through it,
forming a 100% martensitic structure. As the
carbon content increases, so does the hardness of the formed martensite.
Increasing the heat input or preheating the
object to increase the working temperature leads to a lower cooling rate causing the
austenite to transforms at least partially into
softer and tougher structures (curves 2 and
3). An excessive heat input can cause weld
defects and might lead to decreased impact
toughness due to large grain size. To prevent
the forming of hard and brittle microstructures, it is recommended to use preheating and
increased working temperature instead of
raising the heat input.
Curve 4 represents the cooling rate after
rolling or normalization which usually leads
to a tough ferritic-pearlitic structure even on
high strength structural steels. However,
a completely ferritic-pearlitic structure can
be achieved in welding usually by using
S355J0 grade or softer, for example S275JR
or S235JR.
Back to Table of Contents
13
Curve 1:
• low effective heat input Q; e.g. ø2.5 mm
rod. Q = ca. 0.6 kJ/mm
• martensitic microstructure
• high risk of cracking
Curve 2:
• higher effective heat input Q; e.g. ø4 mm
rod. Q = ca. 1.5 kJ/mm
• in addition to ferrite and perlite, the
microstructure has martensite
• significantly lower risk of cracking
Figure 3. Continuous cooling transformation
(CCT) diagram
A = austenite
F = ferrite
P = pearlite
B = bainite
M = martensite
Ms = martensite transformation starts
Mf = martensite transformation finishes
A3 = A3 –temperature (850 °C)
A1 = A1 –temperature (723 °C)
HV = Vickers hardness
14
Back to Table of Contents
Curve 3:
• high effective heat input Q or increased
working temperature; e.g. ø5 mm rod,
Q = ca. 2.5 kJ/mm or 200 °C working
temperature, ø4 mm rod
• microstructure has parts of ferrite, pearlite
and bainite
• very low risk of cracking
Curve 4:
• cooling path after rolling or normalizing
• ferritic-pearlitic microstructure
• no risk of cracking
4 – WELDABILITY
The term weldability defines how suitable the
material is for welding. Steel is considered
to be highly weldable when a required filling
weld can be done without extra measures. If
the steel’s weldability is poor or restricted and
the weld is done without necessary arrangements, different problems may occur during
the welding process or later in the use. The
most significant of these welding metallurgical problems are:
•
•
•
•
cold cracking
hot cracking
lamellar tearing
deterioration of impact toughness.
The most common one of these is a cold
crack, which can occur in welding of hardening low- and high alloy steels.
The next chapter talks about the defects mentioned above, what causes them and how to
prevent them.
4.1 Cold cracking
The risk of cold cracking is present in the
welding of high strength and other low alloy
steels in particular. The following factors are
preconditions for cold cracking to occur:
• brittle microstructure in the HAZ, mainly
martensitic
• too much hydrogen in weld
• mechanical stresses in weld
Cold cracks can occur as a result of all the
above after the weld has cooled to under 150
°C. Removing any of these preconditions is
usually enough to prevent cold cracking from
happening. Different cold cracking types are
shown in Figure 4. Usually cold cracks occur
on the HAZ, but on high strength steels they
may also appear on the weld metal itself. Cold
cracking is also known as hydrogen cracking,
delayed cracking or underbead cracking.
Figure 4. Different cold cracking types
Cold crack appearance
A In HAZ
1. Underbead crack
2. Root crack
3. Toe crack
B. Weld metal
4. Root crack
5. Transverse crack (usually requires alloyed
filler metal)
4.1.1 Microstructure
When steel hardens, the microstructure
transforms into martensite. Hardening requires a fast enough cooling rate and certain
alloying.
The hardness and toughness of the martensite depend on the carbon content. The martensite
Back to Table of Contents
15
becomes harder and more brittle as the carbon content increases. For example, a carbon
content of 0.2% has a hardness of about 470
HV and a 0.4% has about 640 HV.
Martensite softens and its toughness increases when it is annealed.
The transformation of martensite and its
final content on the HAZ depend on steel’s
hardenability and cooling rate. Higher carbon
content and other alloys cause martensite to
form easier.
In addition to a possible martensite structure,
the HAZ can also include other less dangerous structures. Martensite may appear
locally or on very narrow areas which makes it more difficult to recognize the microstructure.
4.1.2 Hydrogen content
Hydrogen can dissolve into the weld in several ways. It dissolves into the weld pool as
ions, but as the weld cools and steel solidifies,
it turns atomic.
Significantly less hydrogen can dissolve into
solid microstructures than molten ones. From
the weld metal, hydrogen diffuses to the HAZ.
During the cooling, hydrogen atoms attempt
to unite to form hydrogen gas. Some of the
gas leaves the steel and some of it segregates at small openings the steel’s crystalline
structure has, particularly in the welds and its
surroundings. The pressure of the hydrogen
gas can get very high, sometimes to several
thousand bars. Hydrogen’s pressure causes
openings to grow, which build up into cold
cracks.
Hydrogen can get into the weld fro m rod
coatings, flux and flux core, impurities of the
welding wire, rust, snow, ice, paint, grease,
dirt or simply from humidity in the air. Usually the filler material is the main source of
the hydrogen.
16
Back to Table of Contents
With different welding processes, diffusible
hydrogen (HDM) varies. Typical HDM values
with each process are s hown below.
Welding process
and filler metal
Diffusible hydrogen
HDM (ml/100g
deposited weld metal)
MMA
Rutile rods
20-30
Basic rods
3-15
MIG/MAG
Solid wire
1-5
FCAW
Rutile filler
3-5
Basic filler
2-5
Metallic
3-5
filler
SAW
3-15
The cellulose and rutile covered rods have a
high hydrogen content, which is why they are
recommended only for welding of the S235JR
and S275JR –grade steels.
Basic rods are also known as low hydrogen
rods. As the base concentration in the rod
increases, the hydrogen content in the weld
decreases. Basic electrodes are prone to
absorb moisture. To prevent this, they should
be stored correctly and if necessary, dried
following the manufacturer’s instructions.
Moisture resistant rods are also available.
They are much less likely to absorb moisture
from the surrounding air than ordinary basic
rods. Flux used in submerged arc welding
must be stored and dried following the manufacturer’s instructions.
Solid wires have a lower tendency to absorb
moisture, but it may cause rust damage to
them. The optimal processes to achieve low
hydrogen content are MIG/MAG and TIG
welding. Using a lower working temperature, these processes make the welding of high
strength steels possible.
4.1.3 Stresses
Stresses are one of the factors contributing to
the forming of cracks. Most of the stresses are
caused by the welding itself. Locally heated
areas try to expand but the surrounding cold
material prevents this, causing the hot areas
to upset.
In contrast, cooling causes the steel to shrink,
leading to tensile stresses sometimes as high
as the yield point. The problem is emphasized
on rigid structures.
Stresses can be reduced by using a considerably lower strength filler metal or an increased working temperature. After the welding,
stresses can also be reduced with a stress
relieving heat treatment. However, if the weld
has cooled down before the stress relieving,
it does not affect the cold cracking tendency
(see next chapter 4.1.4 Temperature).
On rigid structures, the problem can possibly
be amended with minor structural changes
and by using the correct welding sequence
(see chapter 7 “Weld distortions”).
4.1.4 Temperature
Cold cracks develop after the temperature
drops to about 150 °C. Cold cracking requires
hydrogen to diffuse, which happens at temperatures as low as room temperature. Cracks
may develop as late as 1-2 days after the
welding. For this reason, the inspections are
usually done 24 hours after the welding.
Cold cracking can be prevented by maintaining the increased working temperature
of 150 °C long enough after the welding (so
called dehydrogenation heat treatment, or
DHT). The temperature needs to be maintained long enough, sometimes for several
hours, for the hydrogen to travel away from
the weld. An alternative s olution is to perform a stress relieving without letting the
weld cool to under 100 °C.
4.1.5 Preventing cold cracking
By choosing a highly weldable steel (low
carbon equivalent), suitable joint type and
lowest strength filler metal as possible, cold
cracking can be prevented as early as the
planning phase. In repair welding, the previously mentioned factors cannot usually be
exploited.
The most effective way to prevent cold cracks
is to use low hydrogen fillers, correct welding
parameters and if necessary, preheating and
interpass temperature. As the steel’s strength
and thickness increase, more attention needs
to be paid to the welding processes and
consumables.
The procedures to prevent cold cracking and
ensure an adequate weld are listed below:
Clean the groove of any ice, moisture, rust,
grease, dirt or paint.
Use low diffusible hydrogen fillers, store the
fillers correctly and dry them if necessary.
More information about the filler metals and
their storing is available through their manufacturers.
As the material thickness increases, more
heat must be delivered to the weld. In other
words, arc energy (AE) must be increased,
which can be achieved by lowering the welding speed.
Hydrogen leaves the weld quickly if the temperature is raised. By preheating the object,
the working temperature increases which
prevents hydrogen induced cracking (HIC).
The suitable working temperature is usually
100-300 °C, depending on a steel’s grade.
Microstructures susceptible to hydrogen embrittlement can be detected, for example with
a hardness test. Usually a hardness under
350 HV does not cause problems. If very low
hydrogen fillers are used, even 400 HV may
be acceptable. If the welding is done using an
increased working temperature, even 450 HV
can be acceptable.
Stresses make the weld more susceptible to
hydrogen embrittlement. The risk is extra
Back to Table of Contents
17
high in the welding of thick materials and
rigid structures, which is why filler metal that
are too strong should not be used. A general
rule is that the filler metal’s strength should
not be more than 5-10 % higher than the base
material’s.
Use of an austenitic or undermatching filler
metal is also possible if the properties of the
weld allow it.
4.2 Hot cracking
Hot cracks, also known as solidification
cracks, develop in high temperatures (over
1200 °C) as the weld solidifies or right after.
The most common type is a longitudinal
crack on the centerline of the weld. It can
appear on the weld’s surface or just below,
either as a separate crack or starting from a
crater crack, Figure 5. Because of the oxidation, the fracture surface is bluish.
Figure 5 – Hot cracks. 1: crater crack and 2:
longitudinal crack. Narrow and deep bead
increases the risk of hot cracking.
The main factors behind hot cracking are the
shrinking of the weld as it cools and solidifies, along with a gathering of the alloys and
impurities at the weld’s centerline. A narrow
and deep bead, high transversal stresses and
certain impurities increase the hot cracking risk.
Filler metals usually contain very few impurities. However, impurities from the base material can mix into the weld metal. Sulphur and
phosphorus are particularly problematic, as
they form liquid films. These films, which solidify in low temperatures, are located on the
center of the weld, which is last to solidify. A
narrow and deep weld bead increases the risk
of hot cracking, as it causes the solidification
front to advance horizontally and perpendicularly from the fusion boundary to the weld’s
centerline, where the impurities and compounds with low melting points gather up.
Hot cracking appears particularly in processes with a deep penetration such as a MIG/
MAG and SAW. The welds of the free machining steels are also susceptible to hot cracking due to their high sulphur content.
For estimating the susceptibility of the hot
cracking on ferritic steels, a formula based
on chemical composition has been developed. The Units of Cracking Susceptibility
(UCS) was originally developed for the SAW
process, but it can also be applied to other
processes. The following guidelines lower the
risk hot cracking:
• The depth of the bead needs to be smaller
than the width.
• A high manganese filler metal binds the
harmful sulphur into a harmless
manganese sulfite.
• Low arc energy results into a small
penetration, reducing the dilution.
• By lowering the welding speed.
• With pulsating, the weld can be “mixed”,
which prevents impurities from gathering
at the centerline of the weld.
• Improve the fitting so the root gap is smaller.
UCS = 230 C + 190 S +75 P + 45 Nb – 12.3 Si – 5.4 Mn – 1
UCS < 10
UCS = 10 to 30
UCS > 30
18
(8)
no risk of hot cracking
low risk, which increases as the depth/width ratio increases, welding speed
is high or root gap is wide
high risk of hot cracking
Back to Table of Contents
4.3 Lamellar tearing
Lamellar tearing is related to rolled steel’s
features in the thickness direction. If the weld
joint is shaped in a way which causes high
tension through-thickness, the chance for
lamellar tearing exists. Typical spots for the
lamellar tearing and tearing mechanism are
shown in Figure 6.
Steel’s toughness through-thickness depends
on a number of inclusions and their shape.
Elongated inclusions decrease the toughness
in direction of thickness.
Lamellar tearing risk can be reduced with the
following ways:
• Using high power (by welding through the
whole plate, if possible)
• Increasing the groove’s area
• Using the right bead sequence
• Welding a buttering weld with a tough,
low-strength filler metal
Figure 6 – Typical locations for lamellar
tearing and tearing mechanisms
Back to Table of Contents
19
5 – WELD DEFECTS
The previously covered weld defects, cold and
hot cracking, and lamellar tearing are related to a steel’s limited weldability. The flaws
actually related to the welding performance
are the following:
On a gas-shielded arc welding, wind or a draft
may weaken the gas shielding. In that case,
the gas flow should be increased, the nozzle
distance shortened and an adequate form of
protection arranged.
•
•
•
•
•
•
•
pores
slag inclusions
lack of fusion
incomplete penetration
spatter and poor arc starts
shrinkage cavity (also known as pipe)
undercut
In MMA welding, pores can be caused by the
moisture or eccentricity of the rod’s covering;
by using an arc that is too long, which results
in an inadequate shielding from the rod’s
covering; or by a welding current that is too
low, which caus es the rod to ignite and burn
poorly.
The most common defect is a lack of fusion,
followed by the pores and incomplete penetration.
Moisture in rods, especially when using low
welding currents, causes pores. Basic rods, in
particular, are susceptible to moisture.
5.1 Pores
Pores are caused by gases that got trapped
in the weld, as they did not escape before
the molten pool solidified. Pores can appear
either alone or in larger groups. They are
usually round or elongated, from which an
example can be seen in Figure 7. The reasons
behind the pores are:
Impurities on groove surfaces are a common
cause for pores. Rust, mill scale, grease, dirt,
moisture and paint are harmful in welding
and increase the chances of developing pores.
• an inadequate gas or slag shielding
• moist filler metal
• impurities on the groove surface (dirt,
paint, grease, rust, moisture, etc.)
base material’s segregations and high
sulphur content
• solidification that happens too quick
• use of welding current that is too low
• using arc that is too long
5.2 Slag inclusions
In multipass MMA welding, sometimes the
previous run’s slag does not melt properly, leaving slag trapped between the layers.
However, normally the arc melts the slag
completely. An example of slag inclusions is
on Figure 8.
Figure 8 – An elongated pore
(or a wormhole)
Figure 7 – An elongated pore
(or a wormhole)
20
Back to Table of Contents
Slag inclusions develop when slag gets caught
on sharp and narrow cavities. An incorrect
weaving motion causes an undercut to the
groove’s sidewalls, on which the slag sticks
and can be seen as slag lines on radiography.
Sharp notches between weld layers may also
cause slag inclusions. The root’s and passes’
cross section should be concave. Slag removal
is also easier from a smooth and concave
surface.
Lack of fusion can be prevented by using high
enough power, positioning the arc correctly
so it melts the weld area, and making sure
that the molten pool does not get in front of
the arc.
When welding thick steel objects with rods
that are too thin, slag lines form easily. The
problem can be solved by using a rod with
the correct diameter so the weaving motion
doesn’t grow too wide. Slag inclusions can
also be avoided with a correctly aligned and
shorter arc.
Lack of fusion is a hazardous defect for the
weld’s strength and fatigue life, and it is not
accepted in the welding classes B or C.
Slag inclusions may also occur if the next
pass is done with a current that is too low or
a traveling speed that is too high, which does
not produce enough heat to melt the previous
run’s slag. Rutile rods have a higher tendency
to cause slag inclusions than basic rods because of their slag’s higher melting point.
Thorough slag removal is a cornerstone of a
high quality multi-pass weld. Gas arc weld
processes are known to form little slag, which
is why slag removal is not always necessary
after each weld layer. Nonetheless, careful
slag removal guarantees a high quality weld.
5.3 Lack of fusion
Lack of fusion is a result of poor mixing of
the weld and base material. It may occur if
the heat input is insufficient for melting the
base material and the molten filler gets on the
cold groove surface, preventing the arc from
penetrating into the base material, Figure 9.
Figure 9 – Lack of fusion
5.4 Incomplete penetration
A typical root defect is an incomplete penetration at the weld’s root. This is caused
by a root gap that is too small, a rod with a
diameter that is too large, an arc that is too
long or by a fault in the welding performance. The penetration might be incomplete,
like in Figure 10, or the root fusion might be
incomplete, like in Figure 11. A defect can be
avoided by placing the rod deep enough in
the groove at the start point or by grinding
the joint part.
Figure 10 – Incomplete penetration
Figure 11 – Incomplete root fusion
Back to Table of Contents
21
In large structures, the groove fittings are
often poor and achieving complete penetration from only one side is difficult. The root
needs to be opened deep enough to remove
all possible defects.
5.5 Spatter and poor arc starts
Spatter weakens the structure’s appearance.
If a flawless surface is pursued, it should be
protected. Spatter can be caused, for example, by the wrong welding parameters,
an arc that is too long, magnetic arc blow or
moist welding rods.
At the spot where the arc is started, a small
porous section usually develops, along with
a small hardened area that has small cracks.
Ignition scars also weaken the appearance,
which is why the start should always take place in a groove. The arc is ignited ahead of the
actual starting point, and the porous ignition
area gets welded over, removing the faulty
starting point. Alternatively, ignition scars
can be removed by grinding the surface.
5.6 Shrinkage cavity (or pipe)
Shrinkage cavity, which is shown in Figure 12,
usually develops in the welding of a root run
on the bead’s end. The molten pool solidifies
starting from the groove’s sidewalls, causing
a shrinkage cavity that reaches the surface. A
pipe is often united with a crater crack on the
bead’s end.
Defects can be avoided by reducing the welding current before turning off the arc or by
moving the arc onto an area that is already
welded before turning it off. The pipe needs
to be removed, for example, by grinding or
chiseling the weld before continuing the welding. In SAW welding, the arc can be stopped
over special tabs to prevent pipes from developing to the actual work object.
5.7 Undercut
An undercut is a crater or groove on the weld
groove’s sidewall or on the weld’s toe, see Figure 13. They develop when the base material
melted by the arc drifts away and the filler
metal does not fill the cut.
Figure 13 – Undercut
Typically, undercutting is a result of excessive
current or voltage, an arc that is too long or
poor welding technique. Too short of a stop
on the weld groove’s sidewall or moving the
arc out from the weld groove can easily cause
undercutting.
In fillet welds, if the rod is aligned too upright
or the current or voltage are too high, the undercut develops on the junction of the vertical
plate and weld.
Figure 12 – Shrinkage cavity
If the weld groove angle is narrow when using
a large diameter rod, it may cause undercutting on the V-groove’s sidewalls. Alongside
the undercut develops a slag inclusion, which
can be seen as two uniform slag lines in radiography.
Undercut decreases, in particular, the weld
joint’s fatigue strength.
22
Back to Table of Contents
6 – FEATURES OF A WELD JOINT
The features of a weld joint depend on metallurgical factors along with a joint’s position and shape related factors. For fatigue
strength, the joint position and shape are
usually the decisive factors. Other features
depend more on the welding metallurgical
factors.
Stress concentrations form on the welded
structure, which need special attention when
analyzing the fatigue strength (Figure 14).
Ultimately, the joint’s reliability depends on
all the factors, each with their own weight.
For example, in a brittle fracture analysis, the
toughness of the base material and weld, weld
defects, and notch effect caused by the joint
shape need to be taken into account.
Figure 14 – Stress concentrations on a weld
joint
than the base material to develop in the HAZ.
The area’s width increases as the working
temperature and the heat input increase.
The soft area’s influence on the joint’s strength depends on the area’s geometrical
factors. Stronger material surrounding the
area generates triaxial stress on it, which
increases the yield strength. Because of this,
the strength does not necessarily decrease
despite the soft area, unless the area’s width
is high compared to material thickness.
6.2 Fatigue strength
Stresses’ maximum amplitude and number of
cycles determine if fatigue strength is a critical factor in the design of the welded structure. The limits for the stress range are given
in standard EN 1993-1-9 (2005). Structures
exposed to a number of cycles greater than
the limit need to be designed by using the
fatigue strength.
Steel’s notch sensitivity increases as the
strength increases. The fact that a fatigue
crack’s growth rate does not depend on steel’s strength or microstructure should to be
noticed. The fatigue strength in weld joints
without post-treatment is roughly the same
with all steels after the number of cycles
exceeds 106. The weld bead’s and especially
weld defects’ notch effect and residual stress
have a decisive effect on the joint’s fatigue
strength. The fatigue crack’s starting point in
welded stiffening is shown in Figure 15.
6.1 Static strength
Static strength is usually not a problem in
the weld joints of general structural steels or
those that are similar. Usually, the joint is at
least as strong and tough as the base material.
In the weld joints of hardened, quenched
and tempered, and cold worked steels, the
strength properties need to be taken into
account more precisely.
Welding heat lowers the strength of the steels
mentioned above. It causes an area softer
Figure 15 – Fatigue crack on a longitudinal
joint
Back to Table of Contents
23
Different methods can be applied to increase
the joint’s fatigue strength:
• Grinding, machining, TIG remelting or
ultrasonic impact treating the weld’s edges
lowers the notch effect.
• Sand blasting or shot- or hammerpeening forms compression stress on the
surface, which is beneficial for the fatigue
strength.
• Stress relieving, spot heating, or local
compression and initial overload change
the residual stresses, improving the fatigue
strength.
Structures under fatiguing loads, particularly
made of high strength steels, need special attention on the joint’s shape and position, welding performance, and post-treatment so that
the basic features get optimally exploited.
The required impact toughness depends on
the structure’s use. When the application is
more challenging and the operating temperature is lower, usually in even lower temperatures, a certain impact strength is required.
Usually increasing arc energy lowers impact
toughness by causing a grain growth, by developing brittle microstructures such as bainite
and grain boundary ferrite, and by increasing
impurity concentrations on grain boundaries.
Impact toughness can be improved by increasing the number of passes. In multi-pass welding, the next pass heat treats, or normalizes,
the previous runs, therefore decreasing the
grain size in the heat treated area (Figure 16).
This leads into an improvement of toughness
characteristics.
6.3 Impact toughness
Microstructures developed by welding have
impact toughnesses that vary on a large scale.
Usually the most brittle spot is located on
the fusion boundary, overheated zone or in
weld metal. The simplest and most common
method to measure a joint’s brittle cracking
susceptibility is the Charpy V -impact toughness test.
Figure 16 – Macroscopic specimen of multipass weld
24
Back to Table of Contents
7 – WELD DISTORTIONS
Welding’s high temperatures cause materials to expand. The heated material cannot
expand freely, causing it to upset instead.
The steel is attempting to shrink as it cools,
developing tensile stress into the weld and its
surroundings. Residual stresses can rise, even
as high as the yield point of the steel, which
decreases the fatigue strength.
7.1 Longitudinal and transverse
distortions
Residual stresses cause both longitudinal and
transverse distortions (Figure 17). The size
of the shrinkage depends on the heat input,
number of passes, structure’s rigidity and
groove shape. Along with shrinking, other
distortions such as twisting, angular distortion, bowing and buckling can develop.
Distortions can be prevented with the following actions:
Longitudinal shrinkage:
• Decreasing the heat input
• Multi-pass welding
• Intermittent welding
• Tack welding sequence from the edges to
the center
• Placing the welds symmetrically on the
neutral axis
Transverse shrinkage:
• Decreasing the heat input
• Avoiding excessively large fillet welds
• Using clamps and fixtures
• Correct groove shape, referably X-groove
and double-sided welding
• Short tack welds
• Reducing the root gap
• Backstep welding
• Skip welding
Twisting
• Sufficient tack welding, or welding tacks to
a larger area than the weld
• Using clamps and fixtures
Angular distortion
• Decreasing the heat input
• Correct groove shape
• Reducing the number of passes and
reducing fillet weld’s throat thickness by
increasing the penetration
• Reducing the root gap
• Using pre-angling or pre-bending
Figure 17 – Weld distortions
Back to Table of Contents
25
7.2 Tack welding and welding sequence
The purpose of tack welding is to ensure
correct dimensions in the final structure.
Possible distortions and necessary measures
need to be taken into account in the tack welding phase. Tack welding is recommended to
be done usually with the skip welding technique; by welding tacks sparsely and then returning back between them to weld another.
However, placing a tack weld on the actual
weld’s ending is not recommended. Welding
can be done without using tack welds, if using
suitable clams, jigs or fittings is possible.
The basis of welding sequence planning is
the distribution of stresses and heat, so they
spread as equally as possible in longitudinal
direction, allowing the object to expand and
shrink freely from the object’s center to the
edges.
By using the skipping technique, the whole
structure stiffens and distortions are smaller.
The butt welds should preferably be welded
first.
Due to tack welding’s low heat input, possible preheating needs should be taken into
account to prevent cold cracking.
26
Back to Table of Contents
7.3 Flame straightening
Flame straightening is also known as flame
or heat shrinking. In addition to mechanical
methods, steel can be straightened by using
heat. The temperature must be raised usually to about 650-800 °C to make the plastic
deformations permanent. The heated area
cannot expand due to the cold surroundings,
causing it to upset. As the material cools, it
shrinks, forming a tension which straightens
the structure.
When measuring the steel’s temperature,
either different tactile temperature sensors or
temperature indicating crayons or paints can
be used. Alternatively, the temperature can
be estimated by using the table below.
Steel’s surface color
Temperature °C
Brown red
600
Dark red
650
Cherry
750
Dark orange
900
Yellow
1000
Light yellow
1100
White
1200
8 – WELDING OF DIFFERENT STEEL GRADES
Generally, the welding of steel gets more
challenging as the strength and carbon and
alloy contents increase. Varying heating conditions and cooling rates cause microstructural changes in the weld’s HAZ. This may result in brittle phases, such as coarse-grained
martensite and bainite. Hydrogen’s influence
on the HAZ’s properties gets more harmful as
the steel’s strength increases.
Often in repairs and maintenance, however,
welding of challenging steels cannot be avoided. Also, constructive requirements may
demand welding of high strength, heat-treated steels.
Careful planning and preparation as well as
proper heat treatment possibilities in close
proximity, are vital in successful welding of
such steels. Welding instructions for the dif-
ferent steel groups are given in the following
pages.
From a large selection of filler metals, products from ESAB and Lincoln are used in this
manual. By using filler metal comparison
charts, fillers from other manufacturers can
be chosen.
In MAG-welding, EN ISO 14175 standardized
gas grouping is used, so the correct gases can
be chosen from the products of the desired
supplier.
If the weld joint or welding performance has
special requirements, filler metals that are
different than mentioned can be used. In such
special cases, it is recommended to consult
the filler metal or steel provider.
Gas group
AGA
Woikoski
Composition
M12
MISON® 2*
SK-2
Ar + 2 % CO2
MISON® 2 He*
M13
M20
M21
Ar + 2 % CO2 + 30 % He
CRONIGON® S2
S0-2
Ar + 2 % O2
CRONIGON® He
Awolight
Ar + 30 % He + 1 % O2
MISON® 8*
Awomix
Ar + 8 % CO2
SK-12
Ar + 12 % CO2
MISON® 18*
SK-18
Ar + 18 % CO2
MISON® 25*
SK-25
Ar + 25 % CO2
*Contains also 0.03% NO
Back to Table of Contents
27
8.1 General structural steels
S235JR
S355J0
General structural steels are low carbon-,
non-alloyed- or low manganese steels.
To ensure the fine-grained structure of the
S355J0 grade steel, small amounts of niobium or vanadium can be alloyed to it.
Weldability of the general structural steels
is high with all welding processes. However,
in welding of high material thicknesses, the
risk of cold cracking needs to be taken into
account.
An increased working temperature is recommended in some of tables’ cases.
Recommended consumables for general structural steels
MMA
Steel grade
Filler metal
OK 48.00
OK Femax 33.80
S235JR
Conarc 48
Ferrod 160T
OK 48.00
OK Femax 38.65
S355J0
Conarc 48
Conarc V 180
MAG welding
Steel grade
Filler metal
OK Aristorod 12.50
M21/M20 or CO2
S235JR
OK Aristorod 12.63
M21/M20 or CO2
OK Tubrod 15.14
M21 or CO2
LNM 26
M21/M20 or CO2
LNM 27
M21/M20 or CO2
Outershield T55-H
M21/M20 or CO2
S355J0
28
Back to Table of Contents
Shielding gas
Working temperatures for general structural steels
Steel grade and welding
process
Combined thickness of
the joint, mm
Working temperature, °C
Postweld heat treatment
-120
not increased
Stress relieving, if necessary
120-
150-200
S235JR
MMA
MAG
not increased
S355J0
MMA
MAG
-60
not increased
60-
150-200
-90
not increased
90-
100-200
Stress relieving, if necessary
Heat treatments for general structural steels
Treatment
Temperature, °C
Soaking time, hours
Cooling
Stress relieving
550-600
0.5-2
Slowly to 450 °C, after
which cooling in air
Normalizing
900-930
0.5
In air
8.2 Machine steels
Ovako 520
16Mn5
22Mn5
Ovako 550
The Ovako’s machine steels are further developed from general structural steels. They are
available as round or square bars.
The Imatra machine steels are low carbon
and low manganese alloyed steels (max. 1.5 %
Mn). To ensure a fine-grained structure,
small amounts of vanadium or niobium might
be alloyed to the machine steels. Carbon equivalent CEV ≤ 0.43.
S355J0. For the mechanical properties, the
Ovako 520 meets the requirements for the
S355J2. The steel grade Ovako 520 is comparable to the S355J0 in welding, so it is highly
weldable.
Welding of the 16Mn5 has proven to be
trouble-free, despite the high sulphur content. To prevent hot cracking in challenging
welding constructions, welding is recommended to be done with low arc energy and a high
manganese filler metal. Welding without a
filler metal and with a narrow groove should
be avoided.
From their basic analysis and mechanical properties, they are equal to the grade
Back to Table of Contents
29
The 22Mn5 sulphur content is the highest
of machine steels and its susceptibility to
hot cracking is good to keep in mind as early
as in the designing phase. High heat input,
narrow grooves and stiff structures should be
avoided, in the welding of 22Mn5. The filler
metal’s dilution with the base material should
be paid attention to, so the weld does not
enrich in sulphur.
The Ovako 550 is similar to the Ovako 520
from its basic composition. However, the 550
is cold drawn until Ø 55 mm, which need to
be taken into account in the planning of the
weld and welding itself. The thicker Ø 60-120
mm bars are equivalent to the Ovako 520.
The improved strength achieved with cold
working decreases locally due to the welding’s
thermal effect. Nevertheless, the yield point is
always over 350 N/mm2.
Recommended consumables for machine steels
Steel grade
Ovako 520
Rod
MAG
Shielding gas
OK 48.00
OK Aristorod 12.50
M21/M20 or CO2
OK Femax 38.65
OK Aristorod 12.63
M21/M20 or CO2
Conarc 48
OK Tubrod 15.14
M21 or CO2
Conarc V 180
LNM 26
M21/M20 or CO2
LNM 27
M21/M20 or CO2
Outershield T55-H
M21/M20 or CO2
OK 55.00
OK Autrod 12.51
M21/M20 or CO2
OK Femax 38.65
OK Autrod 12.64
M21/M20
16Mn5
Conarc 49
OK Tubrod 15.14
M21
22Mn5
Conarc V 180
LNM 26
M21/M20 or CO2
LNM 27
M21/M20
Ovako 550
30
Outershield T55-H
M21/M20
OK 48.00
OK Aristorod 12.63
M21/M20 or CO2
OK Femax 38.65
OK Tubrod 15.14
M21 or CO2
Conarc 48
LNM 27
M21/M20 or CO2
Conarc V 180
Outershield T55-H
M21/M20 or CO2
Back to Table of Contents
Working temperatures for machine steels
Welding process
Combined thickness of
the joint, mm
Working temperature, °C
Postweld heat treatment
MMA
-60
not increased
Stress relieving, if necessary
60-
150-200
MAG
-90
not increased
90-
150-200
Stress relieving, if necessary
Heat treatments for machine steels
Treatment
Temperature, °C
Soaking time, hours
Cooling
Stress relieving
550-600
0.5-2
Slowly to 450 °C, after
which cooling in air
Normalizing
900-930
0.5
In air
8.3 High strength structural steels
S400
S500/19MnV5
4CrMn16-4*
High strength structural steels are weldable,
and they are available as flat bars.
The S400 has the guaranteed minimum yield
point of 410 N/mm2 and impact toughness
of KV 27 J at -20 °C. Its weldability is comparable to the grade S355J2 and its carbon
equivalent (CEV) is 0.37 on average.
As a strong but highly weldable steel, the
S400 is well suited for structures and machine components as a supporting and stiffening part. Normally, the S400 is weldable
without an increased working temperature or
postweld heat treatment.
With using the S400, cost savings along with
lighter and smaller structures can be achieved
in comparison to ordinary structural steels.
The S500 is manufactured as a customer product. The strength and impact toughness are
fitted to meet each case’s requirements.
The 4CrMn16-4* is a low carbon, chromium
alloyed steel, which gets its lath martensitic
structure in cooling after the rolling. The
yield point is at least 650 N/mm2. In many
cases, the 4CrMn16-4* is weldable without
increasing the working temperature or performing postweld heat treatment.
Back to Table of Contents
31
Additional instructions for welding of the
4CrMn16-4* are given in pages 42-43. In
welding of the high strength steels, the risk of
cold cracking needs to be taken into account,
see page. 16.
For the high strength steels, recommended
cooling time t8/5 is 5-25 s. In effective heat
input, it equals ca. 1-2 kJ/mm. The exact cooling time depends on the material’s thickness,
and it can be defined by using formulas in EN
1011-2 (2001) standard or by using graphs. If
the cooling time is too short, the risk of cold
cracking increases, and if the cooling time is
too long, the impact toughness decreases.
Recommended consumables for high strength structural steels
Steel grade
Rod
Notes
OK 48.00
OK Femax 38.65
S400
OK 55.00
Conarc 48
Conarc V 180
Conarc 49
OK 48.00, undermatching
S500/19MnV5
OK 74.78
Conarc 48
Conarc 60G
OK 48.00, undermatching
4CrMn16-4*
OK 75.75
Conarc 48
Conarc 80
32
Back to Table of Contents
OK 48.00 and Conarc 48 are nonalloyed filler rods. Using them results
in a weld with a lower strength than
the base material
Steel grade
S400
S500
4CrMn16-4*
MAG
Shielding gas
OK Aristorod 12.50
M21/M20 or CO2
OK Aristorod 12.63
M21/M20 or CO2
OK Tubrod 15.14
M21 or CO2
LNM 26
M21/M20 or CO2
LNM 27
M21/M20 or CO2
Outershield T55-H
M21/M20 or CO2
Notes
Flux-cored wire
Flux-cored wire
OK Autrod 12.64
M21/M20
Undermatching
OK Tubrod 14.12
M21
Flux-cored wire, undermatching
LNM 27
M21/M20
Outershield T55-H
M21/M20
Flux-cored wire
OK Autrod 12.51
M21/M20
Non-alloyed filler wire,
undermatching
OK Autrod 12.64
M21/M20
Non-alloyed filler wire,
undermatching
OK Aristorod 13.12
M21/M20
OK Aristorod 13.29
M21/M20
LNM 26
M21/M20
Non-alloyed filler wire,
undermatching
LNM 27
M21/M20
Non-alloyed filler wire,
undermatching
LNM 19
M21/M20
LNM MoNiVa
M21/M20
Back to Table of Contents
33
Working temperatures for high strength structural steels
Steel grade and
welding process
Combined
thickness of the
joint, mm
Working
temperature, °C
Postweld heat
treatment
-60
Not increased
60-
100-200
Stress relieving, if
necessary
-90
Not increased
Stress relieving, if
necessary
90-
100-200
-20
Not increased
20-
100-200
Stress relieving, if
necessary
-30
Not increased
Stress relieving, if
necessary
30-
100-200
-40
Not increased
40-
100-200
Stress relieving, if
necessary
-60
Not increased
Stress relieving, if
necessary
60-
100-200
Notes
S400
MMA
MAG
S500
MMA
MAG
4CrMn16-4*
MMA
MAG
34
Back to Table of Contents
In stress relieving,
the steel’s strength
slightly decreases
Heat treatments for high strength structural steels
Treatment
Temperature, °C
Soaking time, hours
Cooling
Normalizing
900-930
0.5-1
Stress relieving
550-600
1-2
Slowly to 450 °C,
after which cooling
in air
-hardening
920-950
0.5-1
Quenching in water
-tempering
400-460
0.5-1
In air
Normalizing
930-960
0.5-1
In air
Stress relieving
400-600
2
In air
Notes
S400, S500
Quenching and
tempering
8.4 Quenching and tempering steels
C45
25CrMo4
42CrMo4
34CrNiMo6
4CrMn16-4
Quenching and tempering steels are made for
heat treating, or quenching and tempering.
Therefore, they have a higher carbon content
than weldable structural and machine steels,
between 0.22 and 0.50 %. To improve hardening abilities, the quenching and tempering
steels are alloyed with manganese, chromium, nickel, and molybdenum. Basically, they
all affect welding negatively.
Tempering is not
mandatory
In stress relieving,
the steel’s strength
slightly decreases
The 4CrMn16-4 is exception. Due to its low
carbon content, ca. 0.05 %, the 4CrMn16-4’s
microstructure is lath martensitic.. Unlike
a conventional plate martensite, the lath
martensite is comparatively soft and tough,
making it highly weldable. The Ovako’s quenching and tempering steels are M-treated
to ensure a machinability that is as high as
possible. The M-treatment does not affect
steel’s weldability.
Using the IIW’s formula, the quenching and
tempering steels’ carbon equivalent varies
between CEV = 0.5-1.1 (even though the formula is not meant for estimating the weldability of such steels).
Back to Table of Contents
35
8.4.1 Welding of quenching
and tempering steels
The use of quenching and tempering steels in
welded structures should usually be avoided.
Its comparatively high carbon content and
alloying may cause hardening and cracking
in the welding. In some cases welding cannot be avoided, like in the repair of a broken
structure or when there are constructional
requirements. The welding’s success often
depends on how well the following can be fit
together: steel’s behavior, structure’s rigidity
and postweld heat treatment.
Almost always, the welding of quenching
and tempering steels requires an increased
working temperature, usually 150-400 °C.
The recommended practice (particularly if
the carbon content is more than 0.35 %) is to
choose the working temperature above the
Ms –temperature, or slightly over 350 °C, and
then maintain the temperature at least for an
hour after the welding.
Then austenite decomposition in the weld
leads to softer microstructures, lowering the
cracking risk without significantly lowering
the strength.
Usually the weld needs to be heat treated.
Quenching and tempering is the most recommended treatment. The treatment is most
profitable to do right after the welding before
it cools down. If quenching and tempering after the welding is not possible, a stress relief
needs to be done.
The stress relieving temperature needs to be
chosen slightly under the material’s original
tempering temperature (usually 550-650 °C)
so the strength does not decrease. Annealing
needs to be done as soon as the weld cools
down to 100 °C, so the austenite decomposition is complete. Sometimes, annealing is
not possible right after, and the workpiece
is often sitting at room temperature for long
periods of time before the annealing.
The weld’s cooling needs to be slowed down
(for example, by covering it with mine36
Back to Table of Contents
ral wool) and it must be protected from
draughts.
Welding is always safer to perform on a soft
annealed base material than on a quenched
and tempered base material. The filler metal needs to be selected so that the weld gets
the desired strength after the quenching and
tempering. Nowadays, selecting the filler metal for steels that are already quenched and
tempered and receive only stress relief after
the welding, is not difficult anymore.
Filler metal manufacturers have developed
rods suited especially for quenching and
tempering steels, such as OK 75.75, Conarc
80 and OK 78.16. Also, rods for heat resistant
steels, for example OK 76.18, can be used for
quenching and tempering steels.
To prevent cold cracking, the rods need to
be dried before welding. The recommended
drying temperature is 350 °C and the drying
time should be at least two hours.
If the joint’s strength does not have special
requirements, it is often more beneficial to
weld quenched and tempered base materials
with austenitic stainless steel rods, or over-alloyed rods. Such rods are, for example, OK
67.45, Arosta 307, OK 67.70, Arosta 309Mo,
OK 68.82 and Wearshield BU-30. Equivalent wires are, for example, OK Autrod 16.95,
LNM 307, 309LSi, LNM 309LSi and 312. In
these cases, welding of the 25CrMo4 can be
done even without increasing the working
temperature.
The upside of austenitic filler metals is their
lower susceptibility to cold cracking. Hydrogen is more likely to dissolve in austenite
than in ferrite, making the hydrogen stay in
the austenitic weld and prevent cold cracking
in the HAZ. The yield point of the austenitic
welds varies between 400 N/mm2 and 600
N/mm2.
One way to ease the joining of quenching
and tempering steels, or other low weldability steels, to high weldability steels is to
use buttering weld. Before the actual weld,
a deposition is welded to the junction with a
non-alloyed filler metal. The deposition weld
can also be heat treated, if necessary. After
the deposition weld, the actual welding is performed. The joint’s reliability can be further
increased by stress relieving the structure.
Welding of the quenching and tempering
steels always requires special attention. A
correct weld placement to reduce the structure’s rigidity is important, as well as adequate
heat treatment equipment near the work
area. Usually, the weld’s quality should be
verified with tests.
8.4.2 Welding of the 4CrMn16-4
Unlike conventional quenching and tempering steels, the 4CrMn16-4 is highly weldable,
even after it is quenched and tempered. It
can be welded with the conventional welding
processes and consumables. In MMA welding, both non-alloyed and alloyed rods can
be used, for example, non-alloyed OK 48.00
or Conarc 48 and alloyed OK 75.75 or Conarc
80. The rods must be dried thoroughly before
welding.
Using non-alloyed fillers results in a lower
strength, but the joint’s toughness is better
than with alloyed fillers.
An increased working temperature is usually
not necessary, but in challenging welds, it is
recommended.
4CrMn16-4 does not require postweld heat
treatments.
Low penetration is typical for the 4CrMn164. When the 4CrMn16-4 is welded to a lower
strength steel, the penetration difference
needs to be taken into account. Due to the
4CrMn16-4’s high chromium content, it has a
chromium oxide layer on its surface, reducing
the penetration.
Equal penetration can be achieved by directing the rod so that more thermal effect goes
to the 4CrMn16-4 (Figure 18). A high enough
heat input must be used to ensure adequate
penetration. The simplest way to get a high
enough heat input is to select the highest
values for current from electrode recommendations table.
Of course there are other factors that affect
the penetration, such as correct travel speeds,
root gaps, and rod sizes in relation to a groove
angle.
Figure 18 – To achieve equal penetration
in welding of the 4CrMn16-4 (Imacro) to a
non-alloyed steel, the rod is directed more
towards the 4CrMn16-4 (Imacro).
Back to Table of Contents
37
Recommended consumables for quenching and tempering steels
Steel grade
Rod
Notes
OK 48.00
Non-alloyed rod (soft)
OK 74.78
C45
Conarc 48
Non-alloyed rod (soft)
Conarc 60G
OK 48.00
Non-alloyed rod (soft)
OK 75.75
25CrMo4
OK 78.16
42CrMo4
34CrNiMo6
OK 67.45
Austenitic stainless rod
OK 67.70
OK 68.82
Conarc 48
Non-alloyed rod (soft)
Conarc 80
Arosta 307
Arosta 309Mo
Limarosta 312
OK 48.00
4CrMn16-4 (Imacro M)
OK 75.75
Conarc 48
Conarc 48
38
Back to Table of Contents
Non-alloyed rod (soft)
Non-alloyed rod (soft)
Recommended consumables for quenching and tempering steels
Steel grade
MAG
C45
25CrMo4
42CrMo4
34CrNiMo6
4CrMn16-4 (Imacro M)
Shielding gas
Notes
OK Aristorod 12.63
M21/M20 or CO2
Non-alloyed filler wire (soft)
OK Tubrod 15.14
M21 or CO2
Non-alloyed filler wire (soft)
LNM 27
M21/M20 or CO2
Non-alloyed filler wire (soft)
Outershield 70-H
M21/M20 or CO2
Non-alloyed filler wire (soft)
OK Aristorod 12.50
M21/M20 or CO2
Non-alloyed filler wire (soft)
OK Aristorod 13.12
M21/M20 or CO2
OK Aristorod 13.29
M21/M20 or CO2
OK Tubrod 14.03
M21
Flux-cored wire
OK Autrod 309LSi
M12/M13
Austenitic stainless wire
OK Autrod 16.95
M12/M13
Austenitic stainless wire
LNM 27
M21/M20 or CO2
LNM 19
M21/M20 or CO2
LNM MoNiVa
M21/M20 or CO2
Outershield 690-H
M21
LNM 309LSi
M12/M13
LNM 307
M12/M13
Flux-cored wire
Non-alloyed filler wire (soft)
OK Autrod 12.51
M21/M20 or CO2
OK Aristorod 13.12
M21/M20 or CO2
OK Aristorod 13.29
M21/M20 or CO2
OK Tubrod 14.03
M21
Flux-cored wire
LNM 26
M21/M20 or CO2
Non-alloyed filler wire (soft)
LNM 19
M21/M20 or CO2
LNM MoNiVa
M21/M20 or CO2
Outershield 690-H
M21
Flux-cored wire
Back to Table of Contents
39
Working temperatures for quenching and tempering steels
Steel grade and
welding process
Combined
thickness of the
joint, mm
Working
temperature, °C
-20
50-100
20-
150-200
-20
Not increased
20-
150-200
Postweld heat
treatment
Postweld heat
treatment
C45
MMA
MAG
Stress relieving
Quenching and
tempering
Normalizing
Stress relieving
Quenching and
tempering
Normalizing
25CrMo4
MMA
150-200
Austenitic stainless
filler metal
-20
50-100
20-
150-200
MAG
-20
50-100
20-
150-200
40
Back to Table of Contents
Stress relieving
Quenching and
tempering
Stress relieving
Quenching and
tempering
The weld is softer
than the base material
25CrMo4, 42CrMo4, 34CrNiMo6
MMA
MAG
370-420
Austenitic stainless
filler metal
370-420
Stress relieving
Quenching and
tempering
The working
temperature has to
be maintained 1-2
hours after the
welding, unless
the workpiece is
quenched and
tempered
The weld is softer
than the base
material
4CrMn16-4 (Imacro)
MMA
MAG
-40
Not increased
40-
100-200
-60
Not increased
-60
150-200
Stress relieving, if
necessary
Stress relieving, if
necessary
In stress relieving,
the steel’s strength
slightly decreases
Back to Table of Contents
41
Heat treatments for quenching and tempering steels
Treatment
Temperature, °C
Soaking time, hours
Cooling
840-870
0.5-1
In air
Notes
C45
Normalizing
Quenching and tempering
-hardening
880-920
0.5-1
Quenching in water
or oil
-tempering
550-660
1-2.5
In air
Stress relieving
450-650
2
Slowly to 450 °C,
after which cooling
in air
25CrMo4
Quenching and tempering
-hardening
840-880
0.5-1
Quenching in oil
-tempering
540-680
1-2.5
In air
Stress relieving
450-650
2
Slowly to 450 °C,
after which cooling
in air
42CrMo4, 34CrNiMo6
Quenching and tempering
-hardening
820-850
0.5-1
Quenching in oil
-tempering
540-680
1-2.5
In air
Stress relieving
450-650
2
Slowly to 450 °C,
after which cooling
in air
4CrMn16-4
Quenching and tempering
-hardening
920-950
0.5-1
Quenching in water
-tempering
400-460
1-2.5
In air
Tempering is not
mandatory
Stress relieving
450-600
2
In air
In stress relieving,
the steel’s strength
slightly decreases
42
Back to Table of Contents
8.5 Case hardening steels
The carbon content of a case hardened surface is about 0.7%. Due to this the risk of cold
cracking in the welding of such an object is
very high, and it is best that the welding is
performed before the case hardening.
20NiCrMo2-2
16MnCr5
20MnCr5
17NiCrMo6-4
18NiCrMo7-6
Alloyed case hardening steels are similar to
quenching and tempering steels but their
carbon content is lower, 0.15-0.25 %. Their
weldability in mill state or after soft annealing is comparable to the 25CrMo4.
Just like the welding of quenching and tempering steels, welding of the case hardening
steels requires caution.
If the welding is done after the case hardening, the weld area must be protected from
carbonization or the carbonized layer must be
removed from the weld area.
If the welding is done before the case hardening and the weld also needs to be case
hardened, the filler metal needs to be selected
so it is suitable for case hardening. Such filler
metals are, for example, OK 78.16 or Kryo 3.
Recommended consumables for case hardening steels
Steel grade
Rod
Notes
OK 74.78
OK 75.75
All grades
OK 78.16
Suitable for case hardening
OK 67.45
Austenitic stainless filler rod
OK 67.70
Austenitic stainless filler rod
OK 68.82
Austenitic stainless filler rod
Conarc 60G
Conarc 80
Kryo 3
Suitable for case hardening
Arosta 307
Austenitic stainless filler rod
Arosta 309Mo
Austenitic stainless filler rod
Limarosta 312
Austenitic stainless filler rod
Back to Table of Contents
43
Steel grade
All grades
Rod
Notes
OK Aristorod 13.12
M21/M20 or CO2
OK Aristorod 13.29
M21/M20 or CO2
OK Tubrod 14.03
M21
OK Autrod 309LSi
M12/M13 Austenitic stainless
OK Autrod 16.95
M12/M13 Austenitic stainless
LNM 19
M21/M20 or CO2
LNM MoNiVa
M21/M20 or CO2
Outershield 690-H
M21
LNM 309LSi
M12/M13
LNM 307
M12/M13
Working temperatures for case hardening steels
Welding process (for all
case hardening steels)
Combined thickness of
the joint, mm
Working temperature, °C
Austenitic stainless filler
metal
-20
50-100
20-
150-200
MAG
-20
50-100
-20
150-200
MMA
44
Notes
150-200
Back to Table of Contents
The weld is softer than the
base material
8.6 Boron steels
20MnB4
27MnCrB5-2
30MnB5
38MnB5
Boron is an alloy which strongly increases
steels hardenability. It is alloyed in small
amounts – 0.003 % on average. Other alloys
can be replaced with boron, and with it, the
steel’s carbon content can be lowered without
decreasing the hardening abilities.
Boron steels’ composition is profitable for
welding. Ovako boron steels have relatively
high weldability with their carbon content
being around 0.2-0.3%. On the other hand,
the 38MnB5´s carbon content is 0.4%, and it
is significantly harder to weld.
Boron steels can be welded in either an unhardened or hardened state. The unhardened
(in mill state) boron steels are rather soft,
which is beneficial for welding stresses.
The structures welded in an unhardened state
are either hardened or quenched and tempered after the welding.
In the welding of boron steels, the same general factors as in the welding of high strength
steels need to be taken into account.
The given consumable recommendations lead
to a weld that is slightly softer than the base
material.
If the boron steels are used for rather simple
objects or structures, the working temperatures can be selected from table’s lower end.
In challenging and rigid structures, the working temperature needs to be higher.
Back to Table of Contents
45
Condition and welding process
MMA & MAG
Hot rolled/Unhardened
OK 55.00
Shielding gas
MMA
Conarc 49
MAG
OK Aristorod 12.63
M21/M20 or CO2
LNM 27
M21/M20 or CO2
Hardened
OK 74.78
MMA
Conarc 60G
MAG
OK Aristorod 13.12
M21/M20 or CO2
LNM 19
M21/M20 or CO2
Working temperatures for boron steels
Steel grade and
welding process
Combined
thickness of the
joint, mm
Working
temperature for
simple objects, °C
Working
temperature in
challenging cases
and rigid structures,
°C
-15
Not increased
Not increased
15-30
Not increased
150-200
30-
50-100
150-200
-20
Not increased
Not increased
20-
Not increased
150-200
-20
Not increased
150-200
-20
50-100
150-200
-30
Not increased
150-200
30-
50-100
150-200
-15
Not increased
Not increased
15-
100-200
150-200
-30
Not increased
150-200
30-
50-100
150-200
370-420*
370-420*
Capacity after
processing
20MnB4
MMA
MAG
27MnCrB5-2
MMA
MAG
30MnB5
MMA
MAG
38MnB5
MMA and MAG
* Working temperature is maintained 2 hours after the welding
46
Back to Table of Contents
The hardness of the
hardening steel drops
to around 47 HRC
8.7 Spring steels
40Si7
55Si7
51CrV4
As given by their name, spring steels are
designed to be material for springs. They are
often used in other applications as well, for
example, in wear and structural parts of farm
machinery.
Often in repairs and maintenance work,
problems in the welding of spring steels are
faced. Nevertheless, spring steels must not be
used in supporting structures.
The Ovako spring steel grades 40Si7 and
55Si7 are silicon-manganese alloyed. The
51CrV4 is chromium-vanadium alloyed. Hardenability of the steels increases in the order
mentioned above.
The grades 55Si7 and 51CrV4 have such a
high hardenability, that their welding is not
recommended.
The 40Si7’s carbon content is about 0.4%,
and it is not very highly alloyed, making it
weldable within certain limits.
Sometimes, for example in repairs, it might
be necessary to weld the easily hardening
spring steels 55Si7 or 51CrV4. If the joint’s strength is not a substantial factor, for example
in the welding of a fitting, the welding can be
done using an austenitic filler metal. Cooling
needs to be done slowly.
In welded structures that require high
strength or high abrasion resistance, it is
recommended to use high strength structural
steels or boron steels.
Back to Table of Contents
47
Recommended consumables for spring steels
Steel grade and welding process
MMA and MAG
Shielding gas
Notes
40Si7
OK 55.00
Non-alloyed filler rod
OK 75.75
MMA
Conarc 49
Non-alloyed filler rod
Conarc 80
OK Autrod 12.64
MAG
M21/M20 or CO2
OK Aristorod 13.12
M21/M20 or CO2
LNM 27
M21/M20 or CO2
LNM 19
M21/M20 or CO2
Non-alloyed filler wire
55Si7, 51CrV4
MMA
OK 67.45
Austenitic stainless filler rod
OK 67.70
Austenitic stainless filler rod
OK 68.82
Austenitic stainless filler rod
OK 75.75
Arosta 307
Austenitic stainless filler rod
Arosta 309Mo
Austenitic stainless filler rod
Limarosta 312
Austenitic stainless filler rod
Conarc 80
OK Autrod 309L
MAG
48
M12/M13
Austenitic stainless filler rod
OK Autrod 16.95
M12/M13
Austenitic stainless filler rod
LNM 309LSi
M12/M13
Austenitic stainless filler wire
LNM 307
M12/M13
Austenitic stainless filler wire
Back to Table of Contents
Working temperatures for spring steels
Steel grade
Working temperature,
°C
Postweld heat treatment
Notes
40Si7
100-200
Stress relieving, if necessary
55Si7
51CrV4
600-650
Quenching and tempering,
if possible
Slow cooling from the
working temperature
Temperature, °C
Soaking time, hours
Cooling
-hardening
850-870
0.5
Quenching in water
-tempering
450-650
0.5-1
In air
Stress relieving
400-600
1-2
Slowly to 450 °C, after
which cooling in air
-hardening
830-890
0.5
Quenching in water
-tempering
450-650
0.5-1
In air
Stress relieving
400-600
1-2
Slowly to 450 °C, after
which cooling in air
Heat treatments for spring steels
Treatment
40Si7, 55Si7
Quenching and tempering
51CrV4
Quenching and tempering
Back to Table of Contents
49
9 – REPAIR WELDING OF PROBLEM STEELS
In repairs and maintenance works, it is sometimes necessary to weld steels that are not
meant for it. They might have low weldability
because of their composition or strength, or
sometimes even their origin might be unclear.
Conditions are often unfavorable for welding.
Objects and structures might be so large that
heat treating them is not possible.
Such weldable objects can be, for example,
machine parts such as gears and axles, wear
parts, or tools.
In this brochure, the term “problem steel” refers, for example, to high carbon, quenching
and tempering, spring, case hardening, and
abrasion resistant steels. In the chapter
“Examples of welding the Ovako steels” some
cases like these are covered.
The first thing to do in the welding of a problem steel is to sort out its weldability. It is
simple to do if information about the structure’s composition or strength is available,
for example, through a drawing or material
certificate. The composition and strength of
an unknown material can try to be clarified
through tests such as a spark- or hardness
test. In critical cases, the analysis should be
done, for example, from a sample piece.
If the object’s composition is such that its
welding is covered earlier in steel grade specific instructions, those instructions should be
followed when possible.
The filler metal should be selected so that it
contains the least amount of diffusible hydrogen as possible and is tougher than the base
material, which reduces stresses in the base
material’s HAZ.
50
Back to Table of Contents
With using dried non-alloyed base rods, a
rather tough and soft weld can be achieved.
With non-alloyed rods, an increased working
temperature should be used when possible.
For several years in repair welding of these
steels, welding has been done with austenitic
stainless filler metals, which has been found
to be an excellent method. Heat treatments
are usually not necessary due to a lower risk
of cold cracking and tougher weld metal. As
for such repairing filler metals, many different austenitic or austenitic-ferritic alloys
have been used.
The biggest benefit of an austenitic filler is
its ability to dissolve most of the hydrogen
in the filler-base material mix while avoiding
diffusion into the HAZ where martensite
has formed. The filler metal’s composition is
designed so that a high amount of ferrite can
be alloyed to the weld metal without forming
a microstructure that is prone to cracking.
The most common type of filler metal in
repair welding is 29 % Cr -9 % Ni, and its
composition leads to an austenitic-ferritic structure. The weld metal’s yield point
is about 600 N/mm2, ultimate strength is
about 700 N/mm2 and hardness is about 250
HB. Such filler metals are, for example, OK
68.81, OK 68.82 and Limarosta 312 (see table
below).
Naturally, using an austenitic or austenitic-ferritic filler metal does not prevent the
possibility of the base material’s HAZ from
hardening. An increased working temperature reduces the risk of it happening but it worsens the weld material’s properties. Usually
the welding is done cold.
The most commonly used filler metals in repair welding
18Cr/8Ni/6Mo
23Cr/13Ni
3Cr/13Ni/3Mo
29Cr/9Ni
65Ni/15Cr-Fe-Mn
OK 67.45, OK Autrod 16.95, Tubrodur 200 O D
Arosta 307, LNM 307
OK 67.60, OK Autrod 309LSi, Shield-Bright 309L X-tra
Limarosta 309S, LNM 309LSi, Cor-A-Rosta 309L
OK 67.60, OK Autrod 309MoL, Shield-Bright 309LMo X-tra
Arosta 309Mo, Cor-A-Rosta 309MoL
OK 68.81 and 68.82, OK Autrod 312
Limarosta 312
OK 92.26, OK Autrod 19.85
NiCro 70/15Mn, NiCro 70/19
Back to Table of Contents
51
10 – JOINT WELDING OF NON-ALLOYED AND STAINLESS STEEL
The joint between a non-alloyed and stainless steel is usually welded with a so called over-alloyed stainless filler metal. The
over-alloyed filler has a higher chromium and
nickel content, so it can dilute to a non-alloyed steel without ruining the weld metal’s
qualities.
The filler metal is selected so the following
harmful effects won’t develop: cold cracking,
ferrite grain growth, sigma brittleness or hot
cracking.
In the selection of a filler metal, the Schaeffler
diagram shown in Figure 20 can be used as
an aid. It presents the steel’s microstructure’s
dependence on its Cr- and Ni-equivalents.
The previously mentioned harmful effects
can be avoided by selecting the filler so that
the weld material’s microstructure is on the
bolded area of Figure 20. In addition to the
base material’s composition, the filler metal’s composition and dilution ratio affect the
selection. The dilution ratio tells how much
of the base material is mixed into the weld
metal. Typical dilution ratios for the different
processes are:
Pulsed-MIG/MAG
10-20%
MIG/MAG
20-30%
MMA
20-35%
TIG
20-60%
SAW
40-70%
The given values are approximations since
pre-heating, groove shape, material thickness, filler material diameter, welding current, polarity, arc voltage, travel speed and
arc alignment along with the weld process
affect the dilution ratio.
The forming microstructure can be found on
the line that is connecting the midpoint of
the base materials’ connecting line and the
location of the filler metal, when the dilution
ratio is known.
Non-alloyed and stainless steel can be welded together by using an over-alloyed filler
for the whole groove, or by using buttering
welding. By welding a buttering layer, using
an over-alloyed filler metal, onto the non-alloyed groove surface, the rest of the weld can
be done using a filler metal matching the base
material, Figure 19.
Figure 19 – The joint of non-alloyed and
stainless steel using buttering weld
The most commonly used filler metals are so called over-alloyed type:
23Cr/13Ni/3Mo
OK 67.70
Arosta 309Mo
23Cr/13Ni
OK 67.75
Limarosta 309S
18Cr/8Ni/6Mo
OK 67.45
Arosta 307
29Cr/9Ni
OK 68.82
Limarosta 312
52
Back to Table of Contents
10.1 Example of use
A high strength structural steel, S400, and
an acid resistant steel 18/12/3 (AISI 316) are
welded together. Let us take a closer look
at the filler metals OK 48.00, OK 63.30 and
67.70. The first one’s composition is similar
to a structural steel, the second one is similar
to an acid resistant steel, and the third one is
a so called over-alloyed filler metal.
Even though this example is about a “basic”
high strength structural steel, S400, the
same approach and results also apply to most
non-alloyed and low-alloyed steels.
In the Schaeffler diagram, points 1 and 2
represent the base materials’ Cr- and Niequivalents, and points 3, 4 and 5 represent
the equivalents to the filler metals mentioned
previously mentioned, respectfully.
When the line’s (1,2) midpoint is connected
to points 3, 4 and 5, it can be seen that the
filler OK 48.00 does not hit the triangle in the
middle of diagram. This results in a martensitic microstructure that is hard, brittle and
susceptible to cracking.
Using the filler metal OK 63.30, the dilution
ratios 0-25 % hit the triangle, and with the
filler metal OK 67.70, the dilution ratio is
15-40 %.
It can be seen that with the rod OK 67.70,
the harmful microstructures can be avoided.
Using the rod OK 63.30 might lead to harmful microstructures, and the result is not
reliable.
Figure 20 – Schaeffler’s diagram
Back to Table of Contents
53
11 – HARDFACING
Hardfacing is a process where worn surfaces
or surfaces under high wear are surfaced with
a filler metal, resulting in a surface that is as
or more durable than the structure’s original
material. The method is used both to repair
old structures and make new ones. The purposes of hardfacing are:
During the welding, it is usually recommended to keep the weld object’s temperature,
working temperature, between 200 °C and
500 °C to prevent cracking in the weld metal.
Instructions for selecting the working temperature can be found from catalogs provided
by the filler metal supplier.
• Return the original dimensions to a worn
object so that the renewed object’s service
life may be as long as the original’s.
• To ease manufacturing of complex objects.
Structures that are difficult to make
entirely from a wear-resistant alloy can be
made from a steel that is easier to handle,
and then parts requiring the special
qualities can be hardfaced.
In welding over non-alloyed steels, dilution
needs to be kept in mind. The desired hardness cannot be achieved on the weld’s first
layer.
There are several types of hardfacing rods
and wires with varying features. The selection
is usually made based on the prevailing wear,
weld metal’s hardness and wear resistance.
In addition, the weld metal’s tempering, corrosion, and flaking resistance, etc. need to be
taken into account.
Often, the same object is exposed to several
wear mechanisms which set contradictory
requirements for the material. For example,
high abrasion resistance is difficult to combine with high toughness and good thermal
and corrosion resistance. This is why there
are numerous different hardfacing materials
on the market and why some properties have
to be compromised in order to achieve others.
Some of the hardfacing materials are combinations of several feature requirements.
Table 2 gives a general image of the properties of some hardfacing filler metals. In the
standard EN 14700 (2014), different filler
metals and their suitability for different wear
situations are covered more precisely.
54
Back to Table of Contents
In repair welding of tools and some machine
components, problems may occur. Structural materials are usually hardened and often
harden easily. First it is always safer to sort
out the material’s composition, hardness and
possible heat treatment before the welding.
Then define the welding circumstances:
correct working temperature, suitable annealing method to make the structure weldable,
possible postweld heat treatment, or welding
technique, for example, skip welding.
The weld object’s size is an important factor
in defining the working temperature. Small
objects heat up enough from the arc energy,
sometimes even turning red hot. In this case,
the object should be left to cool down before
continuing the welding because welding when
the workpiece is too hot may lead to a decreased hardness and impact toughness.
Table 2. Filler metals for hardfacing
Back to Table of Contents
55
12 – EXAMPLES OF WELDING THE OVAKO STEELS
In the selection of the following examples,
the goal was to represent different welding
problems and their solutions on a wide scale.
All of the examples have been implemented
in real life, but the best result is not necessarily the one shown in these examples. One
purpose of these examples is to give ideas
and stimulate the development of even more
functional weld joints.
Some of the examples are purely maintenance cases, where the base material selection
might be poor for welding. Although estimating the weldability is a part of the material
selection process, these examples should be
viewed critically and they should not be used
to guide the material selection.
The steels’ properties and their use are covered more precisely on Ovako’s Material Data
Sheets, found in the Steel Navigator.
The design and a stress analysis of the weld
joints are covered in several books and articles. The welding of pressure vessels must
be performed following the rules and regulations given by the authorities and standards.
Steel’s most common groove shapes and their
design are introduced in standard EN ISO
9692-1 (2013).
In addition to instructions for each steel grade, the following general welding rules should
be taken into account:
• Particularly in welding of high strength
steels and rigid structures, the selected
filler metal should be slightly softer than
the base material, or as hard at the most.
• Usually, in welding of two different grades
of steel together, the filler metal should be
selected to match the base material with
the lower strength.
• In the welding of different steel grades
together, the working temperature is based
on the combined material thickness with
the assumption that the whole structure is
made of the more hardening steel.
56
Back to Table of Contents
• In the welding of hardened steels,
exceeding the working temperature of 200
°C causes the structure to soften, and
temperatures from 200 °C to 350 °C
decrease toughness.
• In critical cases, the working temperature
should be maintained for 1-2 hours after
the welding to make sure the hydrogen
has enough time to leave the weld and base
material’s HAZ.
• Particularly in rigid structures, it is
recommended to perform a stress relief. A
correctly done stress relief reduces residual
stresses, improves the weld’s fatigue
strength and toughness, and ensures
permanency of the dimensions in
machining and use.
• Normalization, quenching and tempering,
or some other suitable heat treatment can
also be used as a postweld heat treatment.
The normalization particularly improves
the impact toughness Sin ce the quality of
the weld is always a sum of several factors,
the responsibility of the weld’s success lies
on all: designer, welder and supervisor.
12.1 Flange axle
Structural materials
Flange
Axle
A
Machine steel Ovako 520
Machine steel Ovako 520 or cold drawn machine
steel Ovako 550
B
Machine steel Ovako 520
Quenching and tempering steel 25CrMo4
C
Case-hardening steel 20NiCrMo2-2
Quenching and tempering steel 25CrMo4
Consumables
Rod
A
Wire
OK 48.00
Conarc 48
OK Autrod 12.51
LNM 26
Shielding gas
M21/M20 or CO2
Rod
OK 74.78
Working temperature
Heat
treatments
A flange axle dimensioned like
above, can be welded without increasing the working temperature.
With higher material thicknesses,
the need for an increased working
temperature is determined by the
combined thickness of the joint.
Axle can be case
hardened.
Stress relieving
550-600 °C
Conarc 60G
B
Wire
Shielding gas
OK Aristorod 13.12
150-200 °C
LNM 19
M21/M20 or CO2
Back to Table of Contents
57
OK 74.78
Rod
C
Conarc 60G
Wire
OK Aristorod 13.12
LNM 19
Shielding gas
Case hardening
of the flange
before the
welding
M21/M20 or CO2
Grooves are made by turning. The dimension
is based on a strength requirement, in other
words, torque τ. The axle’s end can be fillet
welded, unless the strength requirement demands a single bevel groove.
The cooling after the welding can be slowed
down with a thermal insulation. If the axle is
machined into a gear wheel, it is case hardened before the welding. Weld areas must be
protected from carbonization.
58
200-250 °C
Back to Table of Contents
Fine turning and possible grinding are done
after the welding.
In alternative A, the cold drawn machine steel
Ovako 550 softens due to the welding’s thermal effect. The yield point drops to around
350 N/mm2. The quenched and tempered
25CrMo4 tempers if the axle’s heat treatment
temperature exceeds the original quenching
and tempering temperature. The case hardened gear teeth soften if their temperature
exceeds 250 °C.
12.2 Torsion bar
Structural materials
A
B
Arm
High strength structural steel S400
Hubs
Cold drawn machine steel Ovako 550
Arm
High strength structural steel S400
Hubs
Quenching and tempering steel 4CrMn16-4
For strength, the K-groove is the most optimal.
The cold drawn machine steel Ovako 550 softens due to the welding’s thermal effect.
Consumables
A
B
The yield point drops to around 350 N/mm2
in the heated zone.
The weld must be placed so that the structure’s strength is not affected. Other structure
weakening features, such as keyways, must be
placed outside of the weld’s thermal effect.
Working temperature
Rod
OK 48.00
OK Femax 38.65
Conarc 48
Conarc V 180
Wire
OK Autrod 12.51
LNM 26
Shielding gas
M21/M20 or CO2
Rod
OK 74.78
Conarc 60G
Wire
OK Aristorod 13.12
LNM 19
Shielding gas
M21/M20 or CO2
A torsion bar dimensioned like above, can be welded
without increasing the working temperature. With
higher material thicknesses, the need for increased
working temperature is determined by the combined
thickness of the joint.
Back to Table of Contents
59
12.3 Repair welding of an axle
Structural materials
A
Quenching and tempering steel 25CrMo4
B
Quenching and tempering steel 42CrM04
C
Machine steel Ovako 520
D
ICold drawn machine steel Ovako 550
Consumables
A
Root passes
Filling layers
B
Root passes
Filling layers
C
Root passes
D
Filling layers
Heat treatments
150-200 °C
Stress relieving in 500600 °C or maintaining
the working temperature
2 hours after the welding
400-450 °C
Stress relieving in 540600 °C. Soaking time 2
hours
150-200 °C
Heat treating is not
necessary
OK 48.00
Conarc 48
OK 74.78
Conarc 60G
OK 48.00
Conarc 48
OK 75.75
Conarc 80
OK 48.00
Conarc 48
OK 48.00
Conarc 48
The destroyed part is removed from the axle.
An X-groove provides a good support for the
weld’s start. If the groove is made by flame
cutting, slag and scale must be removed from
the surface by grinding. A turned conical
shaped groove or an X-groove with an angle under 60° may cause root defects or hot
cracks.
60
Working temperature
Back to Table of Contents
Runs are welded alternately to each side. The
first sealing run must be opened before welding the first run on the second side.
With axles smaller than in the example,
alternatives C and D do not require increased
working temperature.
12.4 Gear
Structural materials
Rim
High strength structural steel S400
Web
General structural steel S355J2
Hub
Machine steel Ovako 520
Structural materials
Rod
Heat treatments
OK 48.00
Conarc 48
Wire
OK Autrod 12.51
Stress relieving in 500-600 °C
Soaking time 2 hours
LNM 26
Shielding gas
M21/M20 or CO2
The X-groove for the rims’s butt weld is
machined. The root pass is welded with a Ø 2
mm rod. The first root passes must be opened
and slag must be removed thoroughly. Staggered welding is recommended.
In gas arc welding, a reduced groove angle of
50 ° is used.
Throat thicknesses of the web’s welds are
determined by the strength requirements.
Back to Table of Contents
61
12.5 Lifting pin for vessel’s shell
Structural materials
Lifting pin
Machine steel Ovako 520
Plate
General structural steel S355J2
Consumables
Rod
Working temperature
OK 48.00
Conarc 48
Wire
OK Autrod 12.51
150-200 °C
LNM 26
Shielding gas
M21/M20 or CO2
The groove can be flame cut, in which case
scale must be removed from the surface.
Groove angles smaller than in the instructions may cause root defects even when using
smaller diameter rods or wires.
An increased working temperature is necessary since the cold, massive lifting pin would
cool down the weld too quickly, which could
cause cracking.
62
Back to Table of Contents
The penetration can be improved by directing
the arc more towards the pin.
Cooling can take place in air. If the lifting pin
is smaller, for example Ø 100-150 mm, the
cooling should be slowed down with insulation.
12.6 Piston rod
Structural materials
Arm
Machine steel Ovako 520
End
Machine steel Ovako 520 or General structural steel S355J2
Consumables
Working temperature
OK 48.00
Rod
OK Femax 38.65
Conarc 48
Wire
OK Autrod 12.64
150-200 °C, if d ≥ 80 mm
LNM 27
Shielding gas
M21/M20 or CO2
The root passes are welded with a Ø 2.5mm
rod. Before welding the other side, the root
must be opened. The slag must be thoroughly
removed from the root pass. Welding advances as staggered welding.
In runs closer to the surface, larger diameter
rods can be used to speed up the process.
For diameters d ≥ 45 mm, the groove shape A
is used. A sharp angled groove made by turning is not recommended, since it might lead
to an incomplete root and increase the risk of
hot cracks and pores. In gas arc welding, the
groove alternative C, in a shape of truncated
cone, can be used.
If the piston rod’s diameter, d, is under 45
mm, the groove is made in a shape resembling a slotted screwdriver (groove B in the
figure).
Back to Table of Contents
63
12.7 Piston
Structural materials
Piston
Machine steel 16Mn5
Arm
Machine steel Ovako 520
Consumables
Heat treatments
OK 55.00
Rod
Conarc 49
Wire
OK Autrod 12.64
150-200 °C, if d ≥ 80 mm
LNM 27
Shielding gas
M20 or Argon
Depth of the chamfer, a, on the piston’s head
is determined by the strength requirements.
The groove’s shape on the rod’s end depends
on the piston’s type of action.
64
Back to Table of Contents
Due to the increased sulphur content in
16Mn5, a high manganese filler metal and
low arc energy should be used. Additionally,
in gas arc welding, either argon or M20 gas
mixture should also be used.
12.8 Valve head
Structural materials
A
B
Head
Stainless steel 18/12/3 (AISI 316)
Stem
Stainless steel 18/12/3 (AISI 316)
Head
Stainless steel 18/12/3 (AISI 316)
Stem
Machine steel Ovako 520
Consumables
Rod
A
Wire
Working temperature
OK 63.30
Limarosta 316L
OK Autrod 316LSi
LNM 316LSi
Shielding gas
Rod
B
Wire
M12
OK 67.70*
Arosta 309Mo*
OK Autrod 309Lsi*
LNM 309LSi
Shielding gas
Working temperature not
increased.
Excessive heating of the weld must
be avoided.
M12/M13
*Especially with higher material thicknesses,
only the surface of the non-stainless steel is
beneficial to weld with an over-alloyed filler
metal. After this, the welding can be continued with the case A’s filler metals.
The groove is worked into the shape of a
slotted screwdriver. Use of a turned conical
shaped groove is not recommended since it
may lead to an incomplete root, lowering the
strength.
The root passes are welded with thin rods.
The root is opened and slag is removed
thoroughly. The welding continues as staggered welding.
The object must be kept as cold as possible
during the welding. If necessary, the object
must be left to cool down during the process.
Back to Table of Contents
65
12.9 Welding a stainless spindle to lever arm
Structural materials
A
B
C
Spindle
Stainless steel 18/8 (AISI 304)
Lever arm
High strength structural steel S400
Spindle
Stainless steel 18/12/3 (AISI 316)
Lever arm
High strength structural steel S400
Spindle
Stainless steel 18/12/3 (AISI 316)
Lever arm
Stainless steel 18/8 (AISI 304)
Consumables
Rod
A
Wire
Number of sites
OK 67.70
Arosta 309Mo
OK Autrod 309LSi
LNM 309LSi
Shielding gas
Rod
B
Wire
M12/M13 or Argon
OK 67.70
Arosta 309Mo
OK Autrod 316Lsi
LNM 309 LSi
Shielding gas
66
M12
Back to Table of Contents
Working temperature not increased.
Excessive heating of the weld must be avoided.
Rod
C
Wire
OK 63.30
Limarosta 316L
OK Autrod 316Lsi
LNM 309 LSi
Shielding gas
M12
The groove can be either a fillet (in the figure,
on top of the spindle) or K-groove (underside), depending on the strength requirement.
The working temperature is kept as low as
possible. In multi-pass welding, the weld
must be left to cool down to room temperature between the passes.
A prerequisite for good corrosion resistance
is thorough slag removal, pickling and passivation. If a wire brush is used, the wires need
to be stainless steel. A grinding wheel cannot
contain iron.
Back to Table of Contents
67
12.10 Steering joint
Structural materials
Arm
High strength structural steel 4CrMn16-4*
Pin
Boron steel 20MnB4
Consumables
Working temperature
OK 74.78
Rod
Conarc 60G
Wire
OK Aristorod 13.12
Shielding gas
LNM 19
50-100 °C. Increased working temperature is not
needed.
M21/M20
For the groove, either a fillet or V-groove
can be selected, depending on the strength
requirement. The groove’s throat thickness
depends on the strength requirement. After
working the groove, the pin is hardened.
The filler metal’s yield point 650 N/mm2 is
68
Back to Table of Contents
roughly the same as for 4CrMn16-4. The heat
from the welding does not conduct further to
the pin, so the pin’s hardness stays unchangeable.
See the more detailed instructions for welding the 4CrMn16-4* steels from pages 4243.
12.11 Joint
Structural materials
A
B
Flat bars
High strength structural steel S400
Axle pin
Machine steel Ovako 520, case hardened
Flat bars
High strength structural steel S400
Axle pin
Boron steel 20MnB4, hardened
The welding area on the case hardened pin
must be protected from carbonization.
The weld’s throat thickness, a, is based on the
strength requirement.
Consumables
Rod
A
Wire
OK 48.00
Conarc
OK Autrod 12.51
OK Tubrod 14.12
LNM 26, Outershield T55-H
Shielding gas
Rod
B
Wire
M21 or CO2
OK 74.78
Conarc 60G
OK Aristorod 13.12
LNM 19
Shielding gas
M21/M20
Back to Table of Contents
69
12.12 Track link A
Structural materials
Chain
Boron steel 20MnB4, hardened
Shoe
High strength structural steel S400
Consumables
Working temperature
OK 74.78
Rod
Conarc 60G
Wire
OK Aristorod 13.12
LNM 19
Shielding gas
M21/M20
In the weld joint 1, the fillet weld’s throat
thickness = 4-5 mm.
The weld joint 2 has an X-groove.
70
Back to Table of Contents
50-100 °C in joint 1
Increased working temperature is not
needed in gas arc welding.
12.13 Track link B
Structural materials
Chain
Boron steel 27MnCrB5-2, hardened
Shoe
Boron steel 27MnCrB5-2, hardened
Anti-skid
Concrete steel, reinforcing bar A 400 HW
Consumables
Rod
Wire
Working temperature
OK 74.78
Conarc 60G
OK Aristorod 13.12
50-100 °C
LNM 19
Shielding gas
M21/M20
In the weld joint 1, the fillet weld’s throat
thickness = 3-4 mm. Alternatively, a fully
penetrating K-groove can be used, which is
made on the chain.
The anti-skid (weld joint 2) can be welded
before or after hardening the shoe part. An
increased working temperature is not necessary.
Boron steel 30MnB5 is weldable following the
instructions on pages 50-51. In this case, the
working temperature is 150-200 °C.
Back to Table of Contents
71
12.14 Welded beam
Structural materials
Flanges
High strength structural steel S400
Web plate
General structural steel S355J2
Consumables
OK 48.00
Rod
Conarc 48
OK Autrod 12.51
OK Tubrod 14.12
Wire
LNM 26
Shielding gas
72
Back to Table of Contents
Outershield T55-H
M21 or CO2
In the fillet weld (1), penetration in MMA
welding can easily be lacking; in which case
the web plate is not continuously attached to
the flanges. As the weld cools down, stresses
develop on such points, which may lead to
cracking in the weld’s root.
With web plate thicknesses d ≤ 5 mm, the
groove shape 2 can be used. For full penetration, a 55 ° bevel angle is the most advantageous. The joint’s asymmetry causes distortion α to develop as the weld cools down and
shrinks. This can be avoided with a correct
pre-angling of the plates before the welding.
To prevent root defects, penetration and possible burn through must be observed and the
defects must be fixed.
A K-groove on weld joint 3 leads to a strong
and whole weld which has the most beneficial
state of strain, but is the most expensive.
The high strength structural steel S400 is
well suited for welded beams in which the
strength is used as the design criterion. The
groove selection must be based on approved
design instructions. As the strength requirements increase (Fv, τv, τt), the groove is
selected in order 1, 2, 3
Back to Table of Contents
73
12.15 Welding a crane rail to beam
Structural materials
A
Rail
High strength structural steel S400
Beam
General structural steel S235J0
High strength structural steel S400
B
Rail
High strength structural steel 4CrMn16-4*
Beam
General structural steel S235J0
High strength structural steel S400
A Ø 5 mm rod is used in the welding. In
welding of the 4CrMn16-4* rail, the surface
passes are welded with hardfacing rods so
that the hardness and abrasion resistance are
equal to the base material. Support molds in
the welding are not needed.
The joint can be gas arc welded, if wind and
other circumstances allow it.
74
Back to Table of Contents
Joint 1
Consumables
A
Rod
Rod
B
Surface passes
OK 48.00
Conarc 48
OK 48.00
Conarc 48
OK Weartrode 30
OK Weartrode 30 HD
Wearshield BU-30
Joint 2
Consumables
OK 48.00
A
Rod
OK Femax 38.65
Conarc 48
Conarc V 180
Wire
OK Autrod 12.51
OK Tubrod 14.12
B
LNM 26
Outershield T55-H
Shielding gas
M21 or CO2
Back to Table of Contents
75
12.16 Support wheels, rolls
Structural materials
Machine steel Ovako 520
Consumables
Rod
Heat treatments
150-200 °C, if the wheel’s
diameter Ø > 200mm
Stress relieving in
450–500 °C
OK Weartrode 30
Wearshield BU-30
Wire
OK Tubrodur 35 S M
Lincore 40-O
Shielding gas
76
Working temperature
CO2
Back to Table of Contents
Often it is profitable to make the support
wheel or roll that is under high wear from
highly weldable and machinable steel, for
example the Ovako 520. The wear-resistant
surfacing is then welded on the surface of the
base material. A hot rolled bar can be used as
a blank, until the limit of Ø 200 mm.
With recommended consumables, the wear
surface gets a good combination of hardness
and toughness, as well as a well spread, even
and highly machinable finish.
Because the weld metal’s hardness decreases
as the temperature exceeds 500 °C, excessive
heating must be avoided, particularly in the
welding of small rolls.
The need for an increased working temperature and stress relief needs to be determined
case by case. The decisive factors are the wheel’s size and operating environment. Smaller
wheels, with a diameter of less than 200 mm,
do not require an increased working temperature. Surfacing always develops tensile
stresses on the surface, which are unprofitable for fatigue life. With an increased working
temperature and stress relieving, such tensions can be reduced.
In future repair welds, the surface is turned
bare until reaching the base material, to prevent dilution of the material
Back to Table of Contents
77
12.17 Corrector lever’s surfacing
Structural materials
Machine steel Ovako 520
The hardness of the surfacing layer after tempering in 550 °C is 53-57 HRC.
The layer has good tempering resistance until
500 °C.
Consumables
Rod
Rod
Working temperature
OK Tooltrode 50
Wearshield ME (e)
OK Weartrode 50
Wearshield MM
*If the weld should be whole, an increased
working temperature is necessary. If minor
cracking on the weld’s surface is accepted,
78
300-500 °C
Back to Table of Contents
300-400 °C*
the welding can be done without increasing
the working temperature.
12.18 Shovel loader’s wear plate
Structural materials
High strength structural steel S400
Consumables
Rod
Rod
Working temperature
OK Weartrode 60 T
Wearshield 60 (e)
300-500 °C
OK Weartrode 55 HD
Wearshield MI (e)
300-400 °C*
*If the weld should be whole, an increased
working temperature is necessary. If minor
cracking on the weld’s surface is accepted, the
welding can be done without increasing the
working temperature.
Back to Table of Contents
79
12.19 Axles’s temporary repair weld
Structural materials
A
Quenching and tempering steel 42CrMo4
B
Quenching and tempering steel 25CrMo4
C
Machine steel Ovako 520
D
Cold drawn machine steel Ovako 550
Consumables
A
Rod
B
Rod
C
Rod
D
Rod
Number of sites
OK 68.82
Limarosta 312
OK 68.82
Limarosta 312
OK 48.00
Working temperature not increased.
Excessive heating of the weld must be avoided.
Conarc 48
OK 48.00
Conarc 48
The welding area is cleaned of dirt and the
destroyed, flaked or cracked layer must be
cleaned.
The cold drawn machine steel Ovako 550’s
strength properties do not change significantly if the instructed practice is followed.
The welding is started with a Ø 3.2 mm rod.
An alternating three-pass welding is used.
The second and subsequent layers can be
welded using larger diameter rods.
The damaged axle can be repaired by surfacing and then turning and milling it to the
original dimensions. With a correct filler metal and welding process, the axles’s strength
and toughness remain almost unchanged
To prevent distortions, the workpice should
be kept as cool as possible during the welding. After the welding, the object can cool
freely in air or covered.
80
Back to Table of Contents
12.20 Gear tooth’s temporary repair weld
Structural materials
Case hardening steel 20NiCrMo2-2
Consumables
Rod
OK 68.82
Limarosta 312
The repaired tooth’s strength and wear resistance should be as high as possible, and the
shape must be possible to mill.
The damaged tooth’s root is cleaned by grinding it. Caution is needed so that damaging
the adjacent teeth is avoided.
The filler metal is 29 Cr/9 Ni. The resulting
weld has an austenitic-ferritic microstructure,
which strain hardens.
The weld is practically machinable. In use,
the hardness increases to about 45 HRC.
The passes are welded with Ø 2.5-3.2 mm
rods. The weld has to be maintained as cool
as possible. The adjacent teeth must be protected from spatter.
The tooth’s root’s yield point is about 600 N/
mm2 and hardness is roughly 240 HB.
Back to Table of Contents
81
12.21 Example of friction welding
Structural materials
Test piece A
Quenching and tempering steel C45
Test piece B
Stainless steel 18/8 (AISI 304)
Test pieces A and B were joined together by
friction welding. The welding was done with
a continuous drive friction welding machine. With the correct parameters, both high
strength and ductility can be achieved.
82
Back to Table of Contents
The joint’s strength can be as high as that of
stainless steel, about 870MPa.
13 – WELDING STANDARDS
EN ISO 9606-1:2013
Qualification testing of welders. Fusion welding. Steels
EN ISO 17637:2011
Non-destructive testing of welds. Visual testing of fusion-welded joints
EN 1011-1:2009
Welding. Recommendations for welding of metallic materials. General
guidance for arc welding
EN 1011-2:2001
Welding. Recommendations for welding of metallic materials. Arc welding
of ferritic steels
EN 1011-3:2000
Welding. Recommendations for welding of metallic materials. Arc welding
of stainless steels
EN ISO 17636-1:2013
Non-destructive testing of welds. Radiographic testing. X- and gamma-ray
techniques with film
EN ISO 17636-2:2013
Non-destructive testing of welds. Radiographic testing. X- and gamma-ray
techniques with digital detectors
EN 1708-1:2010
Welding. Basic welded joint details in steel. Pressurized components
EN 1708-2:2000
Welding. Basic weld joint details in steel. Non-internal pressurized
components
EN ISO 17640:2010
Non-destructive testing of welds. Ultrasonic testing. Techniques, testing levels,
and assessment
EN 1993-1-9:2005
Eurocode 3. Design of steel structures. Fatigue
EN 14700:2014
Welding consumables. Welding consumables for hard-facing
EN ISO 2560:2009
Welding consumables. Covered electrodes for manual metal arc welding of
non-alloy and fine grain steels. Classification
EN ISO 3834-1:2005
Quality requirements for fusion welding of metallic materials. Criteria for the
selection of the appropriate level of quality requirements
EN ISO 3834-2:2005
Quality requirements for fusion welding of metallic materials. Comprehensive
quality requirements
EN ISO 3834-3:2005
Quality requirements for fusion welding of metallic materials. Standard quality
requirements
EN ISO 3834-4:2005
Quality requirements for fusion welding of metallic materials. Elementary
quality requirements
Back to Table of Contents
83
EN ISO 3834-5:2015
Documents with which it is necessary to conform to claim conformity to the
quality requirements of ISO 3834-2, ISO 3834-3 or ISO 3834-4
EN ISO 5817:2014
Welding. Fusion-welded joints in steel, nickel, titanium and their alloys (beam
welding excluded). Quality levels for imperfections
EN ISO 6947:2011
Welding and allied processes. Welding positions
EN ISO 9692-1:2013
Welding and allied processes. Types of joint preparation. Manual metal arc
welding, gas-shielded metal arc welding, gas welding, TIG welding and beam
welding of steels
EN ISO 13916:1997
Welding. Guidance on the measurement of preheating temperature, interpass
temperature and preheat maintenance temperature
EN ISO 13920:1997
Welding. General tolerances for welded constructions. Dimensions for lengths
and angles. Shape and position
EN ISO 14175:2008
Welding consumables. Gases and gas mixtures for fusion welding and allied
processes
EN ISO 14341:2011
Welding consumables. Wire electrodes and weld deposits for gas shielded
metal arc welding of non-alloy and fine grain steels. Classification
EN ISO 15607:2003
Specification and qualification of welding procedures for metallic materials.
General rules
EN ISO 15609-1:2004
Specification and qualification of welding procedures for metallic materials.
Welding procedure specification. Arc welding
EN ISO 15609-2:2001
Specification and qualification of welding procedures for metallic materials.
Welding procedure specification. Gas welding
EN ISO 17632:2008
Welding consumables. Tubular cored electrodes for gas shielded and non-gas
shielded metal arc welding of non-alloy and fine grain steels. Classification
EN ISO 17638:2009
Non-destructive testing of welds. Magnetic particle testing
EN ISO 17663:2009
Welding. Quality requirements for heat treatment in connection with welding
and allied processes
84
Back to Table of Contents
14 – GOOD WORKING ENVIRONMENT ENHANCES PRODUCTIVITY
Investing in industrial safety is profitable! Accidents and sickness absences, as a result of
accident, are expensive to companies. In addition to the direct costs, there are also other
expenses such as: time wasted in solving the
situation, delayed deliveries, and overtime
costs to catch up with the schedule.
An absent worker needs to be replaced with
another one. The new worker needs to be
hired and trained, which may cause temporary negative effects on work performance and
product quality. Bad working conditions may
have the same negative effects. Investing in
industrial safety and working environment
motivates employees and thus improves work
results.
14.1 Industrial safety in welding
Due to welding’s certain characteristics, welding has its own challenges and priorities for
safety. In a well-organized workstation, the
welder is not exposed to welding fumes, dust,
radiation or noise, and the risk of an accident
is low.
14.2 Welding fumes
Welding and cutting always produces fumes.
The harmful fumes contain different vapors
and gases, with the vapors being more problematic. Slag-producing processes usually
create more vapors, and gas arc processes
create more gases.
The vapor is formed from particles that
develop in high temperatures as the metals
vaporize. The majority of the vapors, about
90-95%, come from the filler metal. The
vapors from highly alloyed steels and aluminum are the most problematic. The vapors
from stainless steel contain harmful chromium and nickel compounds, of which some are
categorized as carcinogenic. The UV radiation
and heat originating from the arc generate
harmful ozone and nitrogen oxides. They
develop close to the arc and dilute quickly to
the surrounding air.
In addition to the selected welding process,
the volume of the developing vapors can be
lowered by using gases with a low CO2 content, lowering the welding current, optimizing the arc voltage, and decreasing the filler
metal’s diameter.
Ventilation at the workstation must be arranged in a way so that the welder’s exposure
to welding fumes is minimal. The workshop’s
general ventilation is not sufficient enough
for eliminating the welding fumes. Usually
the best solution is a local exhaust ventilation
which filters the air and then releases it to the
atmosphere. Modern units are both powerful
and easy to move.
In the welding of high alloy steels and aluminum, it is recommended to use a personal
respirator as well.
An efficient local exhaust ventilation clears
30-80% of the welding vapors, and with a
respirator, the volume of the vapors can be
lowered 80-95% in MIG/MAG welding.
14.3 Radiation and noise
Welding generates invisible, yet harmful ultraviolet and infrared radiation and so called
visible blue light. The welder must use personal protection against the harmful radiation.
An auto-darkening welding mask is a safe and
comfortable solution, and it speeds up the
work, as constant mask lifting is not needed.
In addition to the welder, other employees
must be protected from the welding’s radiation and noise. Each workstation should
be separated from its surroundings by using
safety curtains or screens.
14.4 Minimizing the risk of accidents
Good order in a workshop improves safety.
Accident risk is lower when tools, hoses, cables, etc. are well organized.
A neat workstation is also more pleasant to
work at, improving workers’ motivation and
leading to enhanced productivity and quality.
Back to Table of Contents
85
Local exhaust ventilations
Efficient local exhaust ventilation and lighting for the workstation
Filters
With filtering air cleaners, the air can be cleared of fumes and dust
Protective equipment
Personal protective equipment protects the welder from UV- and IR
radiation
Welding curtains
With curtains, radiation and spatter can be prevented from spreading
to surrounding areas
Noise screens
Screens prevent noise and radiation from spreading to surrounding
areas
Hose reels
Hoses and cables on reels lower accident risk, improve work performance, lower maintenance costs, and make the cleaning of the
workstation easier
86
Back to Table of Contents
87
CO-92 GB 19:11 © Ovako 2019
Disclaimer
The information in this document is for illustrative purposes only. The data and examples are
only general recommendations and not a warranty or a guarantee. The suitability of a product
for a specific application can be confirmed only by Ovako once given the actual conditions. The
purchaser of an Ovako product has the responsibility to ascertain and control the applicability of
the products before using them.
Continuous development may necessitate changes in technical data without notice. This document
is only valid for Ovako material. Other material, covering the same international specifications, does
not necessarily comply with the properties presented in this document.
Ovako 2019
©
www.ovako.com
Ovako AB
SE-111 87 Stockholm, Sweden
Phone: +46 (0)8 622 13 00